How to Calculate Costs on a Garage Conversion. If you're short on livable space but you have a garage, consider converting your garage into a spare room. You can turn it into a den, a master suite or an extra bedroom, depending on your needs.
Figure out what use the room will have, as this will, in large part, determine the cost of the garage conversion. If the new room will be a bedroom, you'll have to build some closet space. Consider the location of the garage door, exterior door, interior door and any windows. If there is a breaker box, washer/dryer hookups or a hot water tank in the garage, you might have to have a licensed professional move them. A less expensive option would be to leave them where they are and build a closet to conceal them.
Decide on what you'd like to do with the existing garage door. You can install French doors or a sliding glass door in its place, or, depending on the construction of your home, you can build it into a wall. This is easier to do if your home is wood-framed as opposed to concrete block. Adding a window to the new wall might be a bit easier as it cuts down on the need for exterior siding.
Take measurements and draw up scaled plans for your garage conversion. Consider the location of power outlets and light switches. You must hire a licensed electrician to run power to the new room if it is not already wired for it. If it already has a finished ceiling and walls, that will save you some time and will cost a bit less.
Visit a home improvement store to see what the necessities cost. If you don't have finished walls or ceilings, price drywall, joint compound, drywall tape and a drywall saw, as well as insulation. Pick out flooring; you have several options here: carpet, wood/laminate, tile or vinyl. If you can't install the floors yourself, you'll have to get an estimate from a flooring company. While at the store, locate the door and window section and decide on what would look attractive in place of the garage door. If you're putting up a wall instead (or including a window), take a look at lumber for framing as well as new siding. Also price lumber for any closets or bathrooms you're adding.
Estimate the space required for a bathroom, if you're adding one. Account for a sink and toilet at the very least; a walk-in shower will save some space if you must allow for bathing in this bathroom. For pipe installation, you'll need to call a plumber as this is not a task you can take on yourself. Call around and get some quotes. You can price fixtures, like a sink and toilet, while at the home improvement store.
Call a company that installs air conditioning and get a quote. Know the square footage of the room and the tonnage of your current HVAC system. You'll need to have a licensed professional run ducting to the new room to have it heated and cooled, and possibly replace the central air system if what you currently have will not sufficiently provide for the additional room.