In reply to Jay83:
I don't think texture is great as it'll wear your shoes out. If it's a (presumably overhanging) bouldering wall, you won't be smearing in the conventional way. If you do, it'll typically be agressive leg drags up the wall from the trailing leg (don't know the word for it, but it propels you up in the opposite direction) and you wouldn't need or want texture.
Moreover, if the footholds are really small, slippery and inconvenient, they constantly force you to place your feet carefully which I'll take as a cumulative training positive.
I used outdoor paint on my plywood as it's in the garden, but I guess in the garage anything will work.
Edit; that's all assuming overhanging!
One more thing, I drilled my t-nut holes in an offset grid fashion (star pattern), and slightly wish I'd just done them as a straight grid pattern (square pattern).
Post edited at 18:36