Obtain permission to build a structure on the property. If you are not the property owner then you need to contact the owner or owners and solicit permission from them for the building. You will also need to obtain permission from anyone with a lien (such as a bank) or a right of way (such as a local government or utility) as the garage may interfere with their rights in the property. If your house is of historical significance and has been declared as such, then permission will be needed from the local property board for any additional construction.
Have a surveyor conduct a professional inspection of your property. You are not just building a garage but also the driveway leading to it. The surveyor will inform you of the grade of the ground and the soil consistency for the best site for the garage and driveway path.
Consult with an architect about your ideas for a two-car garage. Do you want a covered walkway leading to the garage from your home? Will the garage have to deal with coastal weather and snowstorms? How much additional room do you want besides enough for two cars; enough for a small workshop? Does the garage need to blend architecturally with the house or other outbuildings? Make sure to solicit any advice the architect may have.
Ask for bids from various contractors. Most general contractors will be able to construct a two car-garage so there will be substantial competition in most metropolitan areas. Ask for any changes the contractor may want to make, some architects are divorced from the realities of actual construction of their ideas. Select the contractor you think will do the best job, keeping in mind that you will get what you pay for, so the cheapest may not be the best route.
Contact the local utility and cable companies for them to mark the location of pipes on the property. There will be some digging for the cement foundation of the garage but also the driveway. The pipes should be buried deep enough that the construction will not disturb them but it is better to be on the safe side.
Supervise the construction process to make sure the contractor is keeping with the plan and has your approval for any deviations. The construction should take between two to four weeks depending upon the complexity of the building. Brick buildings will take longer due to the manual and laborious nature of brick laying.