Got a ton of ideas from this thread and finished mine a couple months ago.
I'm only doing 5 gallon batches now and I'm batch sparging, but I left room in my build to add a 2nd burner on the top left above the mash tun and enough space to fit a full keg or a much larger brew kettle on top of the right side burner.
My landlord had a few extra ceramic kitchen tiles in the garage that fit perfectly in the spots below my burner and between the burner and the vertical posts. I don't know if they are helping with heat or not, but I figure it didn't hurt. I was actually somewhat worried about the glass sliding door right behind the burner, but I don't know anything about heat conduction. I've brewed 2 batches and it hasn't seemed to be putting off that much heat.