Not done this myself...'YET'...but as soon as i have my own place, theres a bouldering wall going up somewhere, roof joists sound sturdy enough. I'd go with something that has a small vertical section, for starting feet positions, i have seen articulating overhanging sections, these do require knowledge of carpentry/joinery though.
A good thing to do as far as route setting goes is to draw a grid on the board, give each square a reference, then place a bolt/feature in each square, you then have thousands of possible route combinations, have a book handy with some system where you can state (start left foot Square K7 right foot K12, left hand E5 right hand E9 then move left hand to square ???), it sounds complicated but once you have a system and a few routes it gets easy, one of my local climbing walls have this system and a big fat book with years worth of routes, get mates to make routes, challenge each other, make them harder/easier etc.
I'd also advise making a campus board while your at it.
Good luck, post some pics when its done.