You can build the walls on any flat surface, but the shed platform is ideal. Snap chalk lines on the plywood deck, 3-1/2 in. from the edges of the platform, to indicate the inside edge of the walls. Measure to make sure the lines are parallel and 89 in. apart. Then chalk a line down the center (Photo 1). You’ll use this line to make sure the angled top plates meet in the center.
Build the framework for all four walls. To account for the fact that the front and back walls are different from each other (due to the doorframe in the front) and the side walls must both be sloped (to prevent rain from collecting on the roof), each of these will have to be tackled somewhat differently. It’s easiest to construct the back first, the front second, and the two sides last, as shown in the numbered image below. See How to Frame a Wall for more information before you read the instructions below.[5]

how to build a shed