First see if you have to have a permit for this work. If so, you will get into one nightmare, because of all the inspections and the use of pros only.
Are your garage walls unfinished or are the studs exposed?
What is the on center distance between each stud? What ever this distance is, is the width of the insulation you will need in bats. Installation of this is easy, just need a good staple gun and a box knife. I prefer to use hedge shears for the cutting of the stuff.
Is there insulation in the attic above the ceiling? If not, this is a must. you will have to decide on the wall and ceiling R value. the higher the more conditioned air you will save.
On the floor, is it concrete? do you plan to use carpet or vinyl flooring? A pad and carpet will be much easier and less prep work on the dirt and grease on the concrete. If vinyl, the floor must be etched and properly cleaned for the glue or mastic to adhere.
The garage doors, are they one or two seperate ones? The doors and hinges and springs and mounting stuff has to be removed. Be careful with the springs on the doors if they are rolled up over the header of the doors. These are dangerous. Hire a pro to dismantle these.
Is the flooring entering the garage at an angle to make the car's entrance to the garage like a ramp? If so, you need to address this ramp and build it up.
Is the front where the doors are located going to be half brick and then siding or just what? if the bottom section is brick, you have to build forms to remove the angle so that the bricks will go up straight.
Hanging drywall in the garage interior walls. Before you do this, make sure that you are satisfied with the electrical outlets. I am saying this because once you hang the rock, you are committed, installing outlets is very difficult or impossible at this time. Consider, TV outlets, stereo outlets, just whatever.
Patricia, I will now give you a ball park estimate of material based on doing my double garage this way and others.
This estimate is based on brick up one third of the way, a set of windows and masonite siding the rest of the way up. The carpet and pad, we had.
The material ran about $1800. The labor would be around $2500 depending on your eco environment. This was also working without a permit.
If you work with a permit and have to have all those inspections, allow allot more $$$ for all this stuff and for licensed contractors for each step.
Others may have different comments and opinions and that will only help you cover all the bases.