The Clown trousers I made were easy
I just laid a pair of my jeans on to the material and chalked round them but about 2" bigger
Made the legs a lot wider (like flares) so there was enough room for the springs to compress ( look at some pics of people jumping and measure them
I made the trousers about 4" short of the floor and left them as flares ( they don't seem to get caught up)
Worst bit is how much material you need
Jason