What are some of the qualities I should look for in this type of remodeling contractor?
My home is 70 years old and was built without a garage but I could use the extra storage space.

How can I tell if the contractor is bidding to low (and will hit me with costs later or too high because they don't want the project.

Any help would be appreciated.

You want someone with good carpentry skills and access to good concrete people for the foundation of it. Ask around at your village hall for names of companies that focus on garages. When you check references, always go look at their previous jobs. Get a written contract that spells out everything from the type of lumber to the style of the door. Add a clause that says you won't authorize any more charges unless they are agreed to in writing. Make sure the contractor takes out a permit and NEVER pay ahead of the work being done-- a 10 percent downpayment should be fine. If the contractor doesn't have credit to use for buying materials, then you don't want to hire him. Hope this helps!