An easily assembled greenhouse apparatus includes a polymer tube frame formed with plastic tube frame members, some of which have a plurality of openings therein, which tubes are connected together with conventional plastic tube couplings. Each of a plurality of cover attaching members has a screen gripping portion and a tube attaching member for attaching to the polymer tube frame. A plastic covering extends over the polymer tube frame and is attached thereto with the plurality of cover attaching members attaching through the plastic covering and into one of the polymer tubing frame member openings. A door is formed with polymer tube frame members and has a polymer covering and a pair of hinge pins. A method of assembling a greenhouse includes selecting the polymer tubing frame in accordance with the apparatus and rotatably attaching a door formed with polymer tube frame members with a pair of hinge pins, and then selecting a plurality of cover attaching members and attaching a plastic covering extending over the polymer tube frame with the plurality of cover attaching members.