RC Track drivers stand

Im building a Drivers stand for an RC race track, with a Conex as my base. I needs drawings to include the 4 pillars ill construck for the "foundation" these woll be 48" deep and 12" wide, with a 10x10"steel plate with I hooks that go intonthe concrete. The Conex will then be welded to this plates. Then on top of the conex we will construct an 8'x10' enclosed room. The rest of the top deck will be a deck with railing for drivers to use to drive there cars. I have attached my personal drawings as reference. But our county requires drawings with Engineer stamps.