A greenhouse is simply a shell and can't control the climate unless equipment is added to help regulate the environment; this will make the greenhouse suitable for plants year round (Image 1). The heart of the greenhouse is the soil box where the potting and repotting is done. To make a potting box, start with the base of the box, which is made from a 3/4" piece of plywood, 2' square. It's a good idea to paint this piece of plywood--top, bottom the edges--to keep it from rotting (Image 2). For the sides of the potting box, use 1/4"x4" composite wood material; composite material it is very durable against rot and won't split when screws are used to connect the boards.
Lay out three pieces of the composite material, each 2' long. Place two short pieces of board across these three pieces at each end and screws them into the two foot pieces.
Making the side panels for the box is similar to making the back panel. Lay out three more pieces of the composite material, 2' long. Attach one short piece to one end of the longer pieces. Next, three pieces of composite material, each about 30" long, are laid diagonally across the three composite pieces. Draw marks to cut this diagonal piece to fit on the side panel. Cut the angles and screw the diagonal board into place. Next, using the diagonal piece as a guide, cut the excess off of the three composite pieces. You should now have a triangular side piece. To make the other side piece, follow the same steps. Next, attach the diagonal piece in the other direction. Cut off any excess and you should end up with two side pieces, each the mirror image of the other.
Next, take the back and two sides and screw them to each other around the plywood base, then screw them to the plywood.
The only thing left to do is to add a front piece to the box. Measure the distance between the two sides at the front of the box. It should be slightly less than 2'. Cut a piece of composite material to that length and screw it into place.