This is copied from the Colorado DMV website
To register your custom-built car in Colorado, you will first need to apply for a vehicle identification number (VIN). First have it inspected by a member of law enforcement. If it passes the inspection, you will be given a Colorado Certified VIN Inspection form (Form DR 2704).
Next, visit your local Colorado DMV office with:
Once you have your VIN, take the Colorado Certified VIN Inspection form (Form DR 2704) to an emissions testing center. It must pass the emissions test before you can register it. ( If the car is to be titled as a "Kit Car" it will be emissions excempt. (MHCC Comment)
Once this is done, you're ready to have it registered, which is the same process as registration of a standard car or truck. Visit our Colorado Car Registration page for steps.