Measure the area for the new garage
First you should calculate the area where you are planning to build the detached garage. It is preferable to build a garage which can accommodate two or more cars. However, check out your budget before building a spacious detached garage. For your slab foundation you need to make a framework. Then place metal grid work which will strengthen the floor. It is preferable to pour concrete in one go rather than pouring it in sections.
You need to make walls of cinder blocks and in order to hold the bricks, place metal ties into the mortar. Then install beams for windows and doors. Later, install wiring for exterior lightings.
Next you need to hire an extractor to place wooden trusses on the garage roof or to build the wooden frame of the garage roof. Then cover the garage roof with plywood and place metal sheets above. You need to install gutters and downspouts at this stage.
Finish the exterior
You need to brick the exterior walls and paint the exterior wood. Then run the electrical wirings for the whole garage. Install the exterior fixtures after wiring the garage.
In the end you need to install garage and exit doors on the appropriate spaces. Then install all the light fixtures and outlets for work purposes.