Things You'll Need
Instructions
Decide on what kind of vehicle you are building. If you want to make a plane or a train, you may need different types of pieces than if you were building an automobile or truck, or even a spaceship. Look at examples of existing custom creations for inspiration, such as those on the web pages listed below in resources. If it helps, you can sketch a rough idea for your model.
Build the body of the model. Begin with the bottom and underside of the chassis. Most models should be at least four to six studs wide, to accommodate a LEGO Minifig character as either a driver or passengers. The length is determined by the type of vehicle you are building; a spacecraft can be any length, a plane or train will want to be longer than a car or truck. Build this as the foundation of your model.
Build up the outer walls of the model to about half of their final height. Add at least two levels of bricks to the outside of the model to create the body of your vehicle. While building walls, make sure that the upper row's bricks cover any gaps between the neighboring bricks on the lower row.
Put in any seating or controls for your vehicle. LEGO has steering wheels for road vehicles, and a number of angled bricks with controls printed on them. If you cannot find one, you can draw controls onto a sticker and paste it onto the front or side of a brick.
Put any LEGO Minifigs you want to drive your vehicle into the driver's seats. This allows you to build around the figure(s) and make sure they fit, and will also remind you to install a hinge brick or other way to get them out of the model.
Build up the walls of the model so that the Minifig is enclosed in the vehicle, unless you are building a vehicle with a convertible or open roof. Attach a roof to the vehicle made of plate bricks.
Attach the windshield or windows to the front of the vehicle. If you do not have a way to get your Minifig out, some LEGO models have a solution: They connect the windshield to the model using only two studs, and smooth plates around the outside, meaning that the two studs will lock the piece into place, but it will be easy to remove.
Connect your vehicle's means of locomotion. For example, if you have a car, it can't move without a set of wheels strapped to the bottom. If you're working on a plane, it will need wings and a tail section if it's going to get off the ground. A spaceship will need some kind of rocket booster.
Attach any finishing touches to the model -- things like laser cannons, or a spoiler. Again, consult the websites listed under Resources for more suggestions.