If you wish to give it a go at building your own wheels, then i recommend you get hold of one of two books by well known and well respected wheel builders.
The Art of Wheel Building by Gerd Schraner
The Bicycle Wheel by Jobst Brandt
Both detail a different way of building wheels and both have more theory than you can shack a stick at.

If books aren't your thing and you prefer an online guide. Check out Sheldon Brown's guide. Sheldon is the worlds most famous bicycle mechanic. May he forever rest in a wrench filled peace.
Sheldon Brown Wheel Building
Just watch out for his theory on symmetrispokes!

Spoke lenght is an important issue. For this there are a number of online guides avaliable.
DT Swiss Spoke Calc
Edd's Spoke Calc