Quote Originally Posted by artificer View Post
I recommend a small 'tree house' constructed on an I-beam set into a 1' square concrete block. Once you're up off the ground, there's nobody to say you're building over your 'lot line'.
Hate to rain on your parade, but most real estate law provides that you own the 'air space' above and between the boundaries of your land. In your case you would be building in someone else's air space. It is possible to purchase 'air space rights', for example construction over a rail line in places like New York and Chicago.

Brian