Wade
I make them out of plywood. Only because I detest MDF.
It's just a crosscut sled with a platform table at 45 degrees to the blade. I've made them for router tables, and table saws.
The material sets on top of the panel and is clamped in place.
It has limitations for size though. You have to be able to control the wood.
It takes a day or so to make one and a motor shim kit.