Riser thoughts

I am getting ready to construct a riser for my second row of seats and I am looking for some input. The seats are a 3 row set with the dimensions of - 96 in wide X 72 deep (in the fully extended mode) - they are 43 in tall. I have the same seats in the 1st row.

My question is what would be the proper platform size? (width & depth)
I was planning to make it 10 in tall.

Thx for the link. I had seen that in other posts. What I am looking for is a good L x W for the platform top. I am thinking 8ft x 10ft. The extra 2 feet on the width is to prevent the chairs from sitting right on the edge of the platform.

As far as design, I had planned to run: sub out line (in case I add shakers later); electric line for 3 outlets (2 for electric for chairs / 1 open). I plan to fill the inside with R30 insulation. Anyone have any suggestions for anything I may have missed?