Basic shelter from wood and nails 1
When the goal is the most basic of shelter at the lowest cost, some luxuries have to be sacrificed. A roof and walls is as basic as you can get. Even a wooden floor can be beyond absolute necessity. A simple design should include the simplest of material

Solution

Materials: 1"X2"X8', 2"X2"X8',1"X3"X8', 4'X8'X1/4", 1"nails, 1-1/2"nails, 3"nails, plastic. Using the 1X2s and 1X3s and 2X2s, assemble a truss structure for the inner core of the walls for strength and a void for possible insulation fill sourced locally for free. Even dry grass and straw works. Fasten the plywood over the wooden trusses and then fasten the wall and roof sections together. Plastic is secured over the roof and walls for water resistance.