Hi, newbie here! Google brought me to this thread and it has been a great source of inspiration. I've been wanting to build our 5 year-old painted, Myrtle, an above tank basking spot for awhile now. We recently had to take her out and redo all of the silicone seals in her tank due to a massive leak (the tank was a great craigslist score so I'm not complaining), and I figured it would be the perfect time to get one built while everything was drying and we were making sure it would hold water for a few days before putting her back in.
Here is what I came up with. The basking spot is 17" by about 13." The frame is apprx 24" long, 17" deep, and about 13" tall.
I built a frame out of PVC and painted it black. Then I attached the acrylic floor with zip ties.

I used a glue gun to attach rocks to the floor and added in a few decorations we had sitting around from previous fish tanks (I have a 7 y.o., hence the Spongebob)

My husband and I attached pet screen by anchoring it with small screws and then I went all around and sealed it up with the glue gun, after testing its strenght on spare pieces. It holds extremely well.
And the ramp is made of acrylic, with rocks glued on with the glue gun, and it is attached to the floor with zip ties. I secured the water bottle on the bottom of the ramp for flotation and buoyancy. It's working great and supporting her weight.

Myrtle enjoying her rays. It took her a full day to be comfortable enough to stay up there longer than a minute, which I think is pretty good. We're all happy with the outcome!

Her 125 gal tank, which is in some need of plants and fish

She lives on our sunporch, so we can enjoy her out there and from the family room. This is also why there are so many glares and reflections in my pics.

Thanks again to everyone who has posted here! It was a huge help!