JD's Garage Micro
At this point, the transition frames for both sides of the ramp were done. All that was left was the flat bottom framing, and the surfacing of the skating surface and platforms.
For my flat bottom, I decided on ~6'. I wish I could have gone longer to 8' or 10', but the space in my garage and desired size for my platforms forced me to keep it minimal. I say ~6' (approximately 6 feet) because I slightly modified the length to plan my surface so that when the first layer of ply was added, it would fit exactly 4 4x8 sheets of plywood without me having to even cut them to fit. The way I did this was to continue to measure down the transition with a rib support every 8 inches until the ramps center point in the middle of the flat bottom (96 inches from the top of the ramp's transition where the coping would meet).
As I added the second and third layers of skate surface I thought I'd be able to do the same with them, but (as I soon realized made sense) the surface area of the ramp changed due to the added thickness of each layer so I did have to cut the second two layers ever so slightly to fit exactly. If I had realized this before applying any of the plywood layers I might not have bothered being so precise, but I suppose that was just a little experimental planning on my part and the ramp definitely didn't end up any worse off for it.
The flat bottom construction is fairly simple compared to the transition framing so I won't go into as much detail, but you can see from the photos below that I created a flat bottom that was actually two pieces which I bolted together in the middle, then bolted to the transition frames on either end. I used the same type of 1/2" bolts as before to do this, but I did need to use longer 4" bolts to go through 2 2x4's at a time.