Sorry about above...accidentally hit the wrong button. 
Anyway, I cut pieces of plexiglass to the sizes I want...one larger rectangle for the platform itself, and a longer thinner one for the ramp. I affixed the two pieces together using aquarium silicone. It is a very flexible joint, just meant to keep them together. I drilled holes through the plexi on the sides that would be making contact with the tank. I also used a sharp knife to put a small hole or slot in the outer part of suction cups. (The part sticking out where a hook would be.) I attached the suction cups to the sides of the plexi using zip ties. I didn't want to use metal hooks or wire because of the possibility of rusting in the tank. I also attached to the surface of the tank some of that rubbery shelf liner made by Rubber Maid so that when climbing up the ramp, the turtle would have traction. This was attached by smearing a layer of silicone down and then pressing the shelf liner into the silicone.
Before drilling or attaching suction cups, make sure you figure out how many you can squeeze on to a side. I used a medium size cup and was able to 7-8 per side touching the tank. When you put the finished ramp and platform in the tank, make sure the silicone has completely cured (several days) and that you push it into the corner and side of the tank well. Definitely build it for a corner...that way you can get suction cups on multiple sides. I can push down on mine with several pounds of pressure without it budging a bit. If you need more details, let me know.