I make my own pigeon traps. I use 1x2 welded wire for the "cage" section, leaving the bottom open. This allows setting on flat rooftops and the pigeons are not spooked by the unfamiliar "floor". When setting on beams or areas without a flat surface, I use plywood as a base. When setting on plywood base, always secure the traps with a couple screws/clips, as hawks and owls will hit them hard sometimes. If not secured, the trap will be knocked off the base and the pigeons gone. I have found larger traps produce results better than the smaller sizes. 3x5 feet is a good size, providing you have a vehicle to haul them with. I use the pre-made bobs from pigeon supply stores (link below). Pre-baiting helps (with bobs wired open) and the real key is WATER inside, not just bait. That pan inside is for water.... the bait is placed on the floor. Once a pigeon gets inside, leave it there and others will usually enter with much less caution.
http://www.globalpigeon.com/gps.php?action=showprod&id=52