There are a few things you need in order to make a car trailer. The first is a car. Second is some kind of frame or support system to hold the car in place while you build the trailer. Third is some kind of door or window opening that will allow you to access the car inside the trailer. Fourth is a sturdy axle and hitch system that will allow you to transport your car safely and efficiently. Fifth is a roof rack or other means of attaching your vehicle to the frame of the trailer. Sixth is some kind of storage container for your car, such as a box, bag, or crate. Seventh is some means of attaching your vehicle to the frame of the trailer using either straps or clamps. Eighth and last are any necessary tools and materials needed in order to build your Trailer!