As life changes, you might find that the house you bought 10 or 15 years ago doesn't really fit you anymore as your family may have gotten larger. Some people make the move to a bigger house or build an addition, but if you're limited by space issue or the cost for major construction, you could convert your garage into a bedroom or living space. A garage conversion would be cheaper than adding a room onto your house, and may be less intrusive while the construction is being done. It would also be easier to acquire any necessary permits to renovate an existing space than if you were building an addition.
Check with your local zoning board for any permits you'll need for construction as well as regulations regarding the use of your garage.
Design how you want the living space to look. You can hire an architect, use a Computer-Aided Design (CAD) program or design the layout yourself with a pencil and paper.
Decide what electrical, plumbing or heating, ventilation, and air conditioning (HVAC) work will need to be done in the garage and if you're going to hire someone to do these jobs. While you might be capable of doing these jobs yourself, local regulations might require you to hire someone who is certified in those areas.
Inspect the concrete floor and make any necessary repairs. If there are just minor cracks, you could fill them in yourself. However if there's a lot of damage, you may have to get the floor replaced by a professional. To repair cracks, use a hammer and chisel to dig into the floor so that you'd get below the depth of the crack, then fill it in with concrete patching compound (read the label for specific instructions).
Remove the garage door and frame out the area so that you can build out that wall according to your plans. Follow local building codes regarding wall framing so that you know the regulations that cover areas such as the spacing of the studs and how the windows and doors should be framed.
Hire a certified professional to complete any electrical, plumbing, or HVAC work that needs to be done. Even if you have the knowledge to do this yourself, local regulations might require a certified professional to do the job.
Frame out any bare concrete walls by attaching a sill plate (a pressure-treated board) to the floor with masonry screws, then building the frame and attaching it to the sill plate with bolts. If the ceiling isn't finished, run ceiling joists across the framing, nailing them into the framing and the end of the roof rafters. Follow all local building codes regarding the framing.
Install any new doors and windows.
Install drywall on the walls and ceiling where needed, attaching them to the studs with drywall screws.
Paint the walls and ceiling.
Install the new surface for the floor, whether it's tile, wood paneling or carpet.