Just finished up my first summer setup. Made a box that is 12L x 2H x 1.5'W. I used Varanda composite decking, exterior screws/liquid nails glue and pressure treated wood. The extra sub layer that is exposed on either side of the sliding surface will have metal coping, but upon getting the sliding surface done last night we moved it out to the yard and gave it a go, slides like a dream (expensive though..glad that we had a few guys going in on this project expense wise).
I am going to finish it off with some ply sides/some design or just a single color paint.
The run in is just turf over an extended ladder. It wasnt sliding well last night, but today I discovered the magic of little soap and water...now I get as much speed as I could want.