Step 1. The greenhouse base

Once your level greenhouse site has been determined, construct the base from 4"x4" treated, or natural decay-resistant, sawn lumber.
Make an oblong 3000mm (94-1/2") x 2400mm (118") as shown in the drawing.

Fix the lumber together in the corners by using galvanized nails and nail plates.

Check that the two diagonal measurements are equal. If not, make any necessary adjustments. When the diagonals are equal, then the base is square.

Check that the base is level.

Secure the base in place by hammering pegs around the perimeter.

Nail the pegs to the base and trim off any pegs protruding higher than the base timber.