A few years back I made a coracle on a course. It was with the green wood working centre, or somthing similar in name to that. It was basically a frame of green wood slats, clamped and stapled, which then dried, setting a solid structure of which was covered with 'callico' - canvas and finally the canvas was covered in several layers of bitchamen. The bitchamen was of the common 'household type' used to coat the roofs of sheds, etc.
A more 'makeshift' frame can be made using a sort of 'spider's web', consisting of interwoven branches and small sapplings and covered possibly with rawhide.
I'v also seen a rather interesting canoe type craft, of Irish origin I beleive, known as a 'Currah'. It uses the same construction methods mentioned previously with the corracle, of slats of green wood, canvas and a coating of tar.
Coracles aren't exactly the most stable of water craft and I can only describe being in one as sitting in a floating tea cup. I wouldnt reccomend using them in water that dosnt have a strong current.
Sharp.
I know a cloth type material has been used in the past to cover coracles, but im not to sure on the details about that.