240lbs isn't that heavy. 28/32 with 14/15/14 DB spokes and a quality hoop like HED C2 should be fine. A few years ago I built a wheelset like this(using White Industries T11 hubs) for a former NFL linebacker. He weighed about 260#, and rode with the finesse you would expect from a football player. He hasn't had any problems with them not being stiff enough, and zero durability issues.