Well, Newbie here building a 24x56 rink with about 8" of slope. so 12" at deep end and 4" at shallow end. I used 1/2 " plywood with a 2x4 perimeter. Filled it during the big rain storm 2 weeks ago. We had some weather to create a pretty good slab but of course that completely melted with the weather we have had over the last week. Next week looks colder so let's hope we can skate soon.
Thanks,
Joe