Step 1: Installing the Beams
Lag two sets of beams to the tree using a 3/4 diameter x 10" lag screw. The top set of beams will be the floor height of your treehouse. Try to to drill the pilot holes as straight and level as possible. Next install the perimeter beams to the top set o beams and square them up using the 3,4,5 rule. Once the frame is square install your floor joist.