This project is simple and versatile and can be completed with a variety of different materials in different ways. The design I will be showing shall be a car made out of paper on top of a Lego powered base. The final result will look like a simple paper car, but if pulled back the Lego pull-back motor will throw it into motion.

Supplies

~2 sheets of thick paper or card stock
1 long sheet of thick paper or card stock (for this specific car, cardstock or paper of at least 22' by 4')
glue or tape (glue is recommended)
Knife to cut paper (scissors can be used but are not recommended)
cardboard (enough to have a double layer on the base of the car)
Hairdryer (optional)
paint or something to color paper/cardstock
1 Lego Pull Back Motor (optional)
4 Lego wheels
Sufficient Legos to connect all the other legos (Depends on the size and type of car)

Legos for this car specifically: (Numbers correspond to the picture of pieces below)

4: Lego Wheels
2: 15 Hole Planks
4: Washers
1: 7 Hole Plank
10: Cross Stoppers
4: Short Plank Connectors
4: Long Plank Connectors
2: 9 Bent Planks
1: Lego Pull Back Motor
2: Cross Tubes

Step 1: Building the Lego Base

To begin I recommend that you start with the Legos, as however they fit shall determine how your car is built. It is possible to not use Legos in your design, in which case one can create fake wheels with paper, cardboard or anything that can substitute for a wheel. However, if you are intending to use Legos then here are instructions.

Lay all the Legos out
Attach the longest planks (# 2) to the motor (# 9) with a plank (# 4) in between to provide support (using all the long plank connectors (# 7))
Add a plank (# 8) at the front (away from the motor) if one wishes for the front wheels to be higher (use all the short plank connectors (# 6))
Attach the back wheels (# 1) to the motor using a cross tube (# 10) along with 6 cross stoppers (# 5) and 2 washers (# 3)
Attach the wheels (# 1) use the last cross tube (# 10) to the front with 4 cross stoppers (# 5) and 2 washers (# 3)

Step 2: Outline of the Car

Once you have the base built, you should measure the distance between the wheels, the diameter of each wheel, and determine how far you want the car to extend on either side. With this information, you can either create a template by hand or use a program such as google slides to create a design for the outline of your car. Remember when doing this that you should keep the bottom flat and put in tabs that you can use when glueing the sides to the other pieces. When you are designing the car, you should also leave some space for the wheels to move freely. Also, make sure the design is not too complex, else when building it, you will have a hard time. Now note that this is merely a template so that you can get an idea of what your design will look like. These pictures show some examples I created that shows how to optimally create a template in google slides. I will be creating my car using the design at the top right.

Car_Design_Examples.pdf
Download

Step 3: Cutting Out and Setting Cardboard Base

Take a piece of cardboard and cut it so that it is about the same size as the car itself. Then put the car on top of the cardboard and create an outline that follows the frame of the car, and accounts for the wheels, as shown above, you then can cut out the outline. Once you have cut out a piece of cardboard that fits the car, use it to cut out another identical one. Place these both on the bottom and push them till they are flush with the bottom of the frame of the car. It may be beneficial to glue or tape the two pieces of cardboard together. Now you have created the base of the car, which you can build upon to create a car.

Once the base is set, one can leave it like this or put a cardboard brace on the base so that the car will be able to take pressure and impacts. The brace I am adding is the same width as the car and has been cut with tabs so that is can stand next to the motor. The brace can be built at the end once one has the frame, and one can measure the height of the car where the brace is going to be, as this brace needs to fit snuggly inside the car's frame. My brace is 2.5 inches tall, and it perfectly fits inside the frame of the car, allowing one to put pressure on the top to pull back the motor. In the end it should look like the pictures above. If it is still not stable one can put tape around the engine and brace to keep the brace upright and in the correct position. The full rational behind this will be seen later.

Step 4: Cutting Out a Template

Print out one of the designs shown above or one you yourself created. Then cut out the design, making sure not to cut off the flaps. The design that is cut will only be a template, therefore minor mistakes do not matter.

Step 5: Cutting Out the Car's Sides

Now that one has a template for their car, you can place it on the cardstock and get a knife. With the knife carefully cut out an outline of the car on the cardstock (make sure to include the tabs). Then take the template off and carefully cut out the car side. Do this twice so you have both sides of the car. When doing this I do not recommend lightly cutting the joint between the tab and the car's side, as it is unnecessary and weakens it.

Step 6: Cutting Out the Car's Top

Now that you have the sides of the car correctly cut out, one needs the top of the car. This is a fairly simple task. Firstly one needs to take the car's base and put it on the edge of a paper (I am using cardstock), for this car at least 22 inches by 4 inches. Put the base of the car once on either end of the paper to so that the bases longest side is flush with the side that is parallel with the direction you wish to cut in. When the base is flush with one side of the paper draw a line on the paper that is on the far side of the base that is not flush with the paper. Do once on two points and then draw a line connecting the two lines. Once that is done and it seems correct, cut the paper along the line. This piece of paper one cuts shall be glued to both sides of the car to make the top.

Step 7: Glueing/Taping Everything Together

Once you have followed all the previous steps, all that is left is building the car. This is not easy, and using tape may be faster, but less pretty. I started by taking one end of the paper and glueing it to the tabs on one end of one of the sides. I used Elmer's glue since I had some, but if there is a glue that dries faster, then that would be preferable. To speed up the process I used a hairdryer to dry the glue. This was very efficient, although the heat from the hairdryer was somewhat uncomfortable if your hand was in direct contact with the air from the drier. I glued each tab to the top piece all the way to the top part of the back. I stopped here so to start with the other side, else if I had not stopped, then it would have been more difficult. I glued the second side to the same place, and then continue until I had glued the top piece to each tab, and cut off what is left.

Once all has dried and it looks correct, put it on the frame of the car by fitting the wheels through the holes and then lifting up the car's side to allow the Lego Pull Back Motor through. Make sure it fits, and if it is dragging on the floor, make sure that the paper is where it will be once glued. If it is still dragging, one can bend or trim the paper and all shall be fine. Make sure not to worry too much about imperfections, as they can easily be painted or colored over.

Step 8: Painting the Car (Optional)

To paint the car I took the paper frame and used Satin Ink Blue and Gloss Purple from a distance so that only small dots of paint would stick. This way I was able to achieve a more textured and interesting effect. I did this with newspapers under the paper shell so to keep the floor under it clean. On the whole, it was simple and effective and ended up with a nice finish. Especially when one puts it on the car frame and glues the bottom tabs onto the cardboard, completing the car. (something that is helpful when using the car, is giving the car a small push before releasing it so that it goes as far as possible)