Im building a subfloor for a gymnasium. Is this a diferent procedure than building on regular concrete. Im planning on gluing and screwing two layers (one on 45 degree the other on 90 degree) of half inch plywood together. leaving a "1 thick floating subfloor. I also plan on using a 6mil poly vapor barrier. Where i some advice is what to put between the plywood and the plastic.
Please give your thoughts.

Put it on the concrete. Plus I like to use a trowel on vapor retarder under the six mil for extra protection. Six mil may not totally block all MVE so in that case if there is money built into the bid, by all means add the extra protection.

Some guys also like to put 15ib roofing felt over the plastic.

Id put felt below and on top the plastic keeps it from wearing holes thru the plastic while its in service. Of course the big thing is a calcium chloride test that concrete to see where you stand. Just because the slab is old or there doesnt look like a problem doesnt mean your off the hook. testing is cheap (under 20 bucks) so its absolutely 100% necessary no matter what.

thanks for the input. so most people use felt, this is to give cushion, or bounce. The architect is requesting some sort of spring puck to put under plywood.

I know this sounds stupid but when buying the plywood make sure its flat and when shipped on site make sure you lay it flat. Because that will turn into a nightmare quick!

Theres a few different ways to make a gym floor springy. I am not any sort of an expert on this but I do know some wood manufactuers make them. You might want to do some home work on that.