Plan out the production's needs for the set. Read through the script and decide what locations are required and how many sets you have to build. Sets showing a city can be condensed so that one side of the stage can denote one street, and the other side another street. Get creative about set placement to keep building costs down.
Paint any storefronts and building walls on plywood. Doorways can be made by sawing out doors from the plywood and reattaching the pieces with hinges. Add small variations to walls and storefronts. If the play takes place in a rough neighborhood, add graffiti, or if the production takes place in an upscale neighborhood, add advertisements of the time period.
Raise the walls by attaching braces made from two-by-fours to the back of the plywood. Nail two lengths of two-by-four directly to the back of the plywood so that they will stand vertically along the back of the plywood. Nail a second piece, as long as the plywood is tall, to the bracing two-by-fours along the ground. Nail a third piece from the top of the plywood to the far end of the two-by-four along the ground. Sand bags can be placed over the ends of the braces to steady them.
Decide on the picture to use as the backdrop. Most city sets use a city skyline to show that the action takes place in a part of a larger city environment.
Sketch out a grid over the skyline picture and number the columns and letter the rows.
Lay out the backdrop cloth and pencil in a grid with the same number of columns and rows as the grid on the picture.
Paint the city skyline onto the backdrop using the grids as guides to ensure the picture is completely transferred over to the backdrop.