Even though you have said previously that you don't recommend two-story buildings on your blocks, I would like a bit more information. Is that a problem with vertical load or with possible wind shear? It doesn't seem to me that a two-story playhouse is going to weigh any more than a full loaded hot-tub. I am planning on a roughly 10x10 base sitting on 2x8, 16 inches on center sitting on a 32x32 grid of blocks. I'm planning on digging out the area underneath and putting 4 inches of sand and gravel mix under the blocks and adding tie-downs to prevent tipping.

Thanks for any help.

Chances are the problem relates to wind issues more than weight. Something like this might tip over if not well-anchored.