AJS922,
We just had the exact bird cage that you described built by Brian Terry Vinyl. They added a 40' x 18' bird cage onto our Lanai and 28' x 9' of it is over grass, the other end is a concrete patio. The narrow end of the bird cage that encompasses the dogs grass area is secured to a 9" footing that ties into the Lanai concrete. This was all engineered and then approved by the ARC of course. This included moving and adjusting the sprinkles to keep the grass under the bird cage watered. Pretty awesome if you ask me!
Give Wayne Terry a call at 352-365-0068. We just had this job completed in March 2013 so this information is current. And depending on where you live in TV dictates what your easement requirements are. Contrary to popular belief, they are not all the same.
I was also told this could not be done by the good and sometimes uninformed folks on this website. And perhaps it couldn't at one time but with all things, things change...sometimes for the good. Good Luck!
BTF2008
