Want to make a Gen slide - how thick of Alum plate?

Use 1/2"+ aluminum angle on all 4 sides. Depending upon where the legs are located use 12+ gauge plate. Go to a local store and flex some panels to get a feel for what you'll need.

I use a local scrap yard because they cut the plate to size and I can browse around and see what else I don't need. :B

Use several short pieces of al angle to secure slides to the floor.