Best type of metal for turntable platform?

At the moment this platform is for a Project RPM3 with Hana SL. Im planning on upgrading both in the future. I have a wooden floor with a lot of play and too many vibrations. Im currently using a maple wood platform at 16 x 13 x 3 on top of SVS subwoofer feet and was going to put the 2nd metal platform on the bottom (maybe on top) of it. Thought if they were same dimensions and flush it would look and sound better. I was planning in putting something in between also. I have a friend with a CNC machine,  so i can pretty much make any design.

These are great pointers!

Among metals, aluminum is one of the best to dampen resonances.

Are you having footfall problems?

what do you mean by footfall?