Kenn159 - hi, I used to live-trap nuisance raccoon when I was a teenager in NE Ohio. I did this for our local game warden, and you should be able to call yours to see if they offer this service for free in your area. He'd get the complaint call, and I'd get the call from him. I used live traps or "box traps" like you're describing. The bait I used was simply stale bread with honey on it. I caught oppossums as well as raccoons using that type of simple bait.
K2 has a a great point as well...those Havahart (brand name for popular line of live traps) units come in different sizes and you may not have bought one large enough for the critter you're hearing. For a large raccoon, your trap should be at least 48" long with the door opening no less than 18" by 18". The box traps I used were homemade from old road sign-type sheet metal with strong wire mesh over the top, and steel tracks for the door to fall straight down. The treadle used to trigger the door to fall shut was all the way in the back of the trap with just enough room for the bait.
When you place that trap, try to ensure it won't fall through your ceiling should you get something large enough that it can roll the trap over...if you think you know where the critter's getting inside the house, try placing the trap outdoors near that area. The stale bread & honey bait never seemed to attract birds, stray dogs/cats, or squirrels for me. However, it will catch other oppossums/raccoons that are within smelling distance of the bait. Just because you catch one doesn't mean you've got the one in the house if the trap's outdoors.
Finally - be sure to have good, thick leather gloves when handling the trap when something's in it. Whatever you catch will want out and will try to grab, claw, and/or bite anything that gets in range. If the trap you have is all wire mesh, then I'd highly recommend having a burlap bag to slide over the trap before picking it up. It can help calm whatever you've caught while you transport the trap to the release area. (I always took them at least 20 miles away from point of capture.) In 6 years of live-trapping, I only got bit once...but having my fingertip split open from the fingernail to the first joint, all the way down to the bone, was one more bite than I wanted!
As far as the droppings you're seeing from the roof sheathing - I can't help you there. Good luck - and be careful! Jim D/West Point, VA