Item Build

Rylai Item Build DotA

Always get a chicken. Don't be a douche bag, just do it, chances are the rest of your team needs the money more than you do.
Rylai Item Build DotA
If you have to buy wards right away because noone else is going to well then again just do it, it's all for the greater good. Since you won't have much money left I suggest getting a set of tangos and a couple of gg branches, if you need regen after that just use the chicken.
If there's another hero that can buy the first set of wards (and there should be in most games) I suggest you get the items listed above. If you know that you'll be harassed a lot and/or like playing very aggressively you can get an extra healing salve or set of tangos instead of 2 branches. Sometimes starting with a magic stick might also be a good idea, for example if you're laning against a Zeus or Bristle Back.
Another thing I sometimes do is buying tangos for another hero. When we use a Centaur+CM lane in a clan war for example Centaur usually starts off with a stout shield, a quelling blade and a flask and I pass him a set of tangos. That way we don’t have to pass the tangos back and forth all the time. It’s a pretty situational thing though.
Rylai Item Build DotA
If you'd like to go for a different combination of items that's fine, just make sure your team has a chicken and a set of wards.
Rylai Item Build DotA

Rylai Item Build DotA
In most games the first thing you should do once you get 200 gold is upgrading the chicken. Having a crow is simply much better since it's faster and items in a crow are actually safe; I'm pretty sure you'll never see a decent player use a chicken to buy his Sacred Relic from the secret shop. It's always useful, for your team as well as yourself, so you don't have to walk back to the base every time you want to buy a new set of wards.
Rylai Item Build DotA
Around the 6 minute mark your first couple of wards will run out and you will definitely want to replace those. If you can afford it also start counter warding, especially when you know where your enemies have their wards.
Rylai Item Build DotA
The first real item you should buy for yourself are boots. Most heroes get some other items like bracers first but since you're playing support that would delay your boots by too much, you need them for ganking and escaping ganks.
Also grab a tp scroll and keep one for the rest of the game. Crystal Maiden is great for so called "save TPs". Basically anytime an enemy decides to tower dive to kill one of your allies you should tp there as fast as possible and freeze him in tower range. This will often save your ally as well as giving you a good chance to get a kill so always look out for those opportunities. (There are of course situations when you can not save your ally and you'll only suicide in the process, in that case you obviously shouldn't tp.)
Next you should get a Magic Wand. You can get the parts earlier, both Magic Stick and gg branches are great for their price but getting Boots is usually more important than completing the Wand. This means that you might have to (temporarily) drop or sell a gg branch but really, it's not a huge loss.
Rylai Item Build DotA
If needed you can also use the crow to get some regen (tangos or flasks) for both you and your lane mate. Sometimes it is smarter to simply go back to the fountain to heal though, I trust you can make that decision.
Rylai Item Build DotA
The last item I listed as "core" is Urn of Shadows and this item is simply amazing. It provides some survivability, comes in small parts but most importantly it has an incredible active ability that is invaluable when pushing but also great during and after ganks. Many people tend to skip this item when someone else has it already but due to the long cool down I actually think having two per team is ideal, three is still okay. If three of your team mates have it already though you should probably skip it and get a bracer or point booster instead.
Rylai Item Build DotA
Rylai Item Build DotA
Luxury Items
Before I start listing items I just want to make sure the following is clear to everyone: The items listed above really are Crystal Maiden's core items. This might seem to be a very cheap core build but please consider that Maiden will hardly ever get to farm, shouldn't really take any kills from other players and will probably die a lot. Also wards are not a one time investment, they should be bought over and over again to provide map control. When playing Crystal Maiden you might well find yourself walking around with this core build for the entire game, this does not mean you're playing badly, more like the opposite.
Thus, when thinking about further items for Crystal Maiden we have to consider a couple of things: Firstly they should be easy to farm, secondly Crystal Maiden does not have a lot of item slots left over. This is the reason bracers are not usually included in my build and should only be bought if the game goes horribly wrong!
Now, without further ado:
Rylai Item Build DotA
Strength Treads
Treads might seem like a horrible investment at first; the attack speed boost is completely useless and for 50 gold more you could get an Ogre Axe which can be used in a BKB or Aghanim’s. But they have one big advantage: They don’t take up an extra slot and as I mentioned before you won’t have a lot of those left over. Most pros have actually started getting strength treads on Maiden in 6.64, by now phase boots are a decent alternative again though.
Rylai Item Build DotA
Phase Boots
Phase boots are pretty great for getting in range to cast your spells and provide some survivability due to the bonus ms. They're not as good as the old phase boots obviously - armour was far better for Maiden than the extra damage is - but the extra mobility is pretty nice and they come in small pieces.
Rylai Item Build DotA
Point Booster
Point Booster is a very cost efficient item that solves your mana issues and provides some much needed survivability. It’s basically like getting a bracer and a null, just that it requires only one slot which makes it far superior. It is harder to farm for but it's worth it.
Rylai Item Build DotA
Kelen's Dagger
Dagger is great for setting up ganks as well as positioning yourself for a nice ultimate in team fights.
It is usually a good choice if you can somehow farm it very early in the game as it helps your ganking a lot. It’s definitely the best choice of luxury items if someone else on your team is warding for some reason. It doesn't exactly solve your mana issues though consider leaving Nova at level 1 for a while when going for a Dagger.
Rylai Item Build DotA
Black King Bar
BKB is obviously gotten to prevent your opponents from cancelling your ultimate right away. Personally I find it a bit overrated; Freezing Field only lasts a maximum of four seconds anyways and with some good positioning or just a good AoE disable by your team (Ravage, Black Hole) I find it rather unnecessary, especially for the cost. I know a lot of people will disagree here though and if you find yourself being stunned the second you cast your ultimate every time and with a lot of cash on your hands then you should definitely consider it. I also recommend getting it when you have a Pit Lord or Treant Protector on your team as they can stop your enemies from moving and attacking but not from throwing their stuns at you. Ogre Axe being a part of the recipe is fairly nice.
Rylai Item Build DotA
Aghanim's Scepter
Let’s face it; the biggest reason to get this is that it requires a Point Booster which you will probably have already. The stats are decent but the boost to your ultimate isn’t overwhelming. Still, it’s okay when you can land your ultimates consistently (again, Black Hole, Ravage and the like are your friends) but generally there are better items.
Rylai Item Build DotA
Mekansm
Mekansm is a good support item for Crystal Maiden, it just has two disadvantages: Unlike any of the 3 items above it will not help you with your ultimate and it also costs some mana while not increasing your mana pool.
Thus it is best in games when you can not land your ultimate and a BKB will not change this (for example when an enemy Naga always saves her net for you). Either get a Point Booster first or only get one level of Nova when going for Mekansm.
Rylai Item Build DotA
Ghost Scepter
Ghost Scepter is a vastly underrated, yet very, very situational item. Its purpose is to counter well farmed physical damage carries late game when they can kill a support hero like Crystal Maiden with just a few hits.
On the other hand it also makes you very susceptible to nukes thus you have to think carefully about when to buy and use it.
Rylai Item Build DotA
Necronomicon
Necronomicon is obviously a great counter for invisible heroes or heroes with small mana pools that are very reliant on their mana (Leoric, refresher Tide or Treant) and works rather well in Push strats.
However Neconomicon is most effective when you can farm it fast and it doesn't help with Crystal Maiden's ultimate at all thus you should only get it in rather extreme situations, usually there are better Necronomicon carriers on your team.
Rylai Item Build DotA
Boots of Travel
Mobility is extremely important in DotA, especially towards late game when a single push can end the game. Now CM is not exactly the type of hero that after a won team battle can TP to the other side of the map and single handedly take down a tower and a couple of barracks but she can help do so at least. You should only get this very late into the game though; BoT shouldn’t be your first luxury item.
Rylai Item Build DotA
Guinsoo's Scythe of Vyse
Okay, now this is a super, super, super luxury item. I’m pretty sure if you play CM as ward bitch map control technician you will be able to farm this in less than 1% of your games (not counting stomps) but if you can it’s extremely powerful, especially late game.
Rylai Item Build DotA
Again, in most games you will probably end up with your core, treads and a point booster but it's far better to play Crystal Maiden as a true supporter and ending up with few items than aiming for all those big shiny items and taking farm from heroes that need it more than you.