The top plate of the greenhouse was engineered to have the oak pegs like the bottom to “lock” the two side panels and the back panel together. As mentioned in the above paragraph, the front panel rests on pegs glued into the base but is not connected to the top plate. The top plate has a hole cut in it to fit the opening of a small squirrel-cage fan that circulates air into the greenhouse. This cut down on unwanted fungal growth. The circulating air escapes through the 4 holes cut into the top plate where the cords for the grow lights are threaded through. There is a vertical rib of wood hanging down from the top plate where the 4 grow lights are attached. Originally I used Incandescent light bulbs but the heat generated and the power usage was too great. I now have three fluorescents and one incandescent bulb. I found that the one incandescent bulb gives me a good level of heat to keep the tropicals thriving.