Install a concrete foundation for the shed to sit on. Use 2-by-6-inch lumber boards to build a box framework to hold a concrete pour. Be sure to drive 10-inch stakes on the outer sides of the perimeter of the framing to keep the concrete intact while it is drying. Smooth out the concrete with a lumber board before troweling it to a smooth finish.
Construct framework for the plastic shed covering with 2-by-6-inch boards. Build an A-frame unit made of two long sloped sides. With a true A-frame, the sloped sides of the roof also comprise the walls. Another option is to build a rectangular shell with an A-frame roof pitched 45 degrees on each side. Place wall studs and roof rafters 18 inches apart. Leave room for a door opening in the framework.
Simply attach plastic sheeting to this building framework with stainless steel nuts and bolts. Another option is to order pre-molded plastic panels to install. Use plenty of caulking in seams and roof areas to keep out rain. Overlap the plastic wall panels as well to tighten the building. Use plastic garbage cans with tight lids inside the building to store items such as fertilizer or potting soil in case the roof is not leak-proof. You can always install metal versus plastic on the roof to offer better protection against strong winds and hail.
Create a door for the shed by constructing a door with framing cut in an X-shape on both the top half and the bottom half. Cover the door with plastic sheeting to match the shed. Use heavy-duty hinges on the door, so it stays secure over time. If you're building with strong pre-molded plastic doors, you don't need to construct framework. Install a latch to hold the door shut when not in use, and think about installing a lock system if you store valuable items in the shed.
To make mowing around the shed easier, lay boards to create an 18-inch margin around the shed. Fill this space with small rocks or wood chips, so you will not have to mow grass close to the shed walls. Lay a couple of stepping stones at the shed door as well. Even if you hide the shed behind trees or shrubs, the border of rocks or mulch around it will help keep the area neater.