Sometimes the detail or curvature of a design you want on a car is not well suited to using masking tape. The design might need to be symmetrical or the radius is too small to use tape. In cases like this I make my own paint templates to achieve the desired results.
My drawing skills are not great, so when dealing with any kind of graphics I turn to a computer drawing program such as Microsoft's Paint. Any program that will let you import a picture and let you draw on it will work. My preference is an open source program called Inkscape. That said, I import the picture and try to draw my paint layout. I try different things to help me visualize what will be the end result. In this case, it will be a two tone paint scheme. I think you will get the idea of where we are going by looking a the picture below.
Depending what you are after you will need to take a straight on picture of the top and or side of the car. Use this picture to import into your drawing program and start drawing. For me when drawing I do not use the free hand tool. I use shapes and edit them. I usually get better results this way, especially if I am concerned about symmetry. The picture below helps to illustrate what I am trying to convey.
Once I get something that I think will work... I then take the design and paste it in a word editing program like Microsoft's Word. Once the design is pasted in the document I copy it and paste it changing the size and dimensions. This gives me choices about which one is the correct size for the car. Notice the double arc... incorporating this in the design will help me make on the fly adjustments when cutting the template out.
I will then print this document out and find which one is the correct pattern to use. I then cut the pattern out of the paper and test fit it to the car just to make sure. Notice I ended up using a combination of the two arcs when cutting the pattern out.
Once the fit has been checked I then print the document on removable labels.
The label itself tends to be a little thick to adhere completely to the car with ease. So there's a little more do do. I cut a piece of painter tape and tape it down on a clean surface.
I then take the template made from the label and tape that down to the painters tape.
I then pull up the painters tape leaving the label attached and then cut out the pattern like I want it. After it has been cut I separate the painter tape from the label and use the pattern transferred to the painters tape as my paint template.
As you see in the above picture you will need to burnish the edges of tape really well. Then finish taping the car and paint.
Just a little clean up work and you're good to go.