ok so title says it all..

i wanna switch to racks,
but they are a little more than i have to spend at the moment,
and really would rather build them.

i wanted to find out if someone could tell me what kinda of materials i would use?

is there a specific kind of wood, and what does everyone use to heat them?
i know alot of people use flexwatt but i hear more people have problems with it.

any help?