Not to say anyone else is wrong, but I had my 7A on the gear when we installed the wings for the first time (to drill the aft spar holes). Everything was leveled to within the capability of the digital level. In fact, adding or letting air out of one tire or another was used to get it as close to absolute level as possible in the lateral axis. Longitudinal level was just as easy.
After drilling the wing spars and locking them in, the empennage was installed and similarly leveled, including a thin shim on one side. Water levels on wings and tail ensured that wings and horizontal stabilizer were perfectly matched.
Piece of cake (ha ha!).
Biggest plus for having the gear installed was that we could move the plane easily to wherever we wanted to work (in this case, from the garage, where the wings wouldn't fit, to the rear patio, where they would).
Steve