If i'm buying hair extentions from hot topic and i have REALLY short, thin hair how many should i buy?

I have really short, thin hair. Plus it's really layered. The longest goes down to my shoulders.If i'm buying hair extentions from hot topic and i have REALLY short, thin hair how many should i buy?
I have the same problem I am going to try a Lace Wig see the pictures of them below. This is what all the celebrities use and you get to curl it too





http://www.lacewigs.me/LISA-WIG_p_13-85....





http://www.lacewigs.me/SHAUNNI-WIG_p_13-...


You can even put it in a high pony tail


http://www.lacewigs.me/zoomify.asp?catal...








Here is a page that tells you more about what the are


http://www.lacewigs.me/What-Are-Lace-Wig...





Here is a page that tells you how to put them on


http://www.lacewigs.me/How-to-Apply-a-La...





There home page


http://www.lacewigs.me/








and this is a real person with it on


http://www.lacewigs.me/Customer-Photos-and-Testimonies_c_36.html





sorry for ll the links ;)If i'm buying hair extentions from hot topic and i have REALLY short, thin hair how many should i buy?
umm maybe 2 or 3
You shouldn't at all, they're very low quality and it'd be best to invest your money in something salon quality, or at least thicker ';clip-ins.';