I am 6'5 and sit around 250ish. I used to hit 300 pnds. Find a bike that fits nicely. At that size it will be all about comfort. If he likes recumbant bikes great, if not try a freeride geometry bike (slope top tube, compact cockpit and riser bars) It will be easier on the bakc. Basically it comes down to comfort. I like Kona, Giant and Norco for TOUGH bikes at a good price.