How much property can you devote to the garage? A single car garage just doesn't seemto be enough space. How wide of a door was recommended? If you have to go with a single car gatage, try to fit in an 8' wide door.
Here's my idea for a minimum suitable garage: Minimum of 2-car bay with a 16-18' door. Depth should be around 24-26' as you will need a workbench. There should be a minimum of 4-6' between the side walls and the car door. Ceiling height should be at least 10' to allow for a hoist if you want/need one. They are great for doing your own service and will help to "stack" a second car.
Floor shoudl be finished concrete and if local code allows, install a floor drain so you can wash the car inside.
Have sufficent electrical power (220V available and at least 60A service. Provide enough circuits for a large number of outlets (cuts down on the number of extension cords). You'll want lots of light. Flourscent tubes are nice but get cold-weather ballast types for winter time. Recessed cans can work too.
Install a small hot water heater and slop sink. Shop heat will be a needed item if you plan on spending time at night or thru the winter in the shop. Add an inside hose bib and if you go with a hot water heater, have a hot water outlet next to the cold water bib. If the garage will be a separate building, consider a toilet and wash basin.
Toys: fridge for beer, air compressor with air couplers spaced around the garage, stereo/TV (cable a must!), phone line and wall phone, computer connection so you can be on the CAC all the time

, finished painted walls, posters, tool chest with rollers, chest or cart for cleaning supplies,
There's probablt lots of other ideas that others can come up with. Go for as much as you can!!