One of lately deceased members built our out of sheet steel, installed rollers and they are very structurally sound. On June 21 2013 a mini tornado lifted one of the roofs off a traphouse, tossed it a hundred fee end over end and we had a fairly simple job of straightening one corner because of the material used.
The ones that I have seen,were a 2X4 frame covered with barn roofing tin and the sildes and track were the hardware for a big sliding barn door. I don't think that there is a "sliding trap roof kit". It is a matter of what you can make work. If you know a club that has their trap houses set up with a sliding
roof, go take a good look at one and you will be able to build one. It ain't brain surgery.