A solid foundation is important for any building project. As you build a garage, it's important that your properly build the footings for it. Without proper footings, the garage floor can crack and settle. This can lead to problems with the structure itself.
Mark where you intend to put the garage. Make sure the corners are square.
Put a course of 5 cm x 25 cm (2 x 10 inch) timber vertically around the outside perimeter of the garage footings. Hold the 5 cm x 25 cm (2 x 10 inch) timber in place with stakes that you drive into the ground with a sledgehammer. The stakes should be outside the edge.
Do the same for the inside edge when you finish the outside edge. The outside edge and inside edge should be at least 60 cm (2 feet) apart. The centre of these two rectangles should be exactly where you intend for the walls of the garage to be.
Build braces to span across the top of the rectangle for additional support of the boards. This also helps to prevent the footings from being too wide.
Use a shovel to dig a trench under the footings for any drains you need to run after you pour the footings. The same is true for electrical conduits and water pipes. Try not to put the pipes too close to any corner.
Place wooden pieces inside the footings form. Set 2 pieces of rebar in each form on top of the wooden pieces. Tie wire around the rebar and wood to keep the rebar suspended above the ground.
Pour the concrete. Before it sets entirely, set anchor bolts vertically in the cement to use to anchor the wooden walls to the concrete footings. Make sure to centre the anchor bolts.
Let the concrete dry for the appropriate amount of time. Remove the inner forms and backfill the centre of the garage with 2 cm (3/4 inch) gravel.