Building permits are required, in most areas, for the construction of any new structure. Local building codes are the rules which determine how those permits are issued. Don't make the mistake of forgetting to obtain a building permit. Not only will most contractors refuse to work without a permit, but if they do, you could be setting yourself up for some costly headaches down the road. A structure which has been built without the proper building permits can result in heavy fines for the owner, and the city has the option, in many cases, of requiring that you either tear the structure down or make big changes in order to meet code. In addition, your insurance company may refuse to cover any structure which was built without a permit.
Another cost-effecting factor is whether garage construction will be completed as a do it yourself project, through the services of a garage builder, or using a purchased two car garage kit.
For a superior carport design, also consider the following: When building a wood carport, make sure the type timber used is suitable for exterior applications, as well as in-ground applications when making posts. Carport height is important; 7-feet from the finished ground to the underside of the lowest end rafter is standard. The roof fall or slope, should be at least 2-inches; slope should be steeper (about 6-inches) if using clear PVC for the roof so water run-off is faster and roof stays cleaner. A carport size of 20-feet by 10-feet is modest; construct yours bigger if the vehicle (or boat, etc.) you are building it for is large, or if you plan on using it for other purposes in addition to vehicle shelter. For instance, as a place to sit and relax, or to work on hobbies and make repairs, etc. Posts set into the ground in concrete and bolted to the beams (using two bolts at each meeting) usually do not require further bracing. Posts supported by galvanized post brackets alone will require additional bracing for increased stability.
At the other extreme is the homeowner who currently owns a small, sporty car. Not wanting to overspend, he builds a very small garage, thinking that even if he buys another car in the future, he'll be well accommodated. Over time, this homeowner may very well get married and have children. Suddenly, the household isn't well accommodated at all.