I built this flat storage camera rig to get top down shots of my desk. It's basically a large saw-horse that I attach my Joby flexible tripod to and it works great!
The plastic parts were a bit too loose of a fit for the 2x2 beams I bought at Home Depot, so you may want to scale everything down 1 or 2 percent for a tighter fit. I just used a bunch of epoxy, so that works too. Mine is still working great more than 5 years later!
Make sure to refer to my length chart in the photos for the wood pieces to ensure that it comes together correctly, although you can always adjust things for your own needs if you adjust the lengths proportionately.
Watch the process video linked above for detailed assembly instructions