It's pretty easy actually. After you make whatever symbols you want to use for the pattern, you need to decide how large they need to be on the hood and how you want them spaced. In my attached example, I am showing how to create pattern of 1 inch X's and O's that repeat every 10 inches. Open a new file that is 10 inches x 10 inches at 100dpi. Move your guides to divide the space in half vertically and horizontally. Then use your guides to divide each quarter in half again. Note, your pattern source file should have a transparent background. I left a white background so you could see the guides better. Centering your graphics using the guides will ensure your pattern is perfectly spaced. You can use the same graphic or different graphics depending on the look you are going for. Center one graphic in the top left quadrant. Center another graphic in the lower right quadrant. The blank quadrants are what will give your final pattern that staggered look. Experiment with the size and spacing of your pattern source file. Once you get it laid out, in Photoshop choose Edit>Define Pattern. Now your Pattern source file is created.
Now it's time to create the layout for your vehicle hood panel. Make a new document scaled to the size of the hood you are going to wrap. In my example, for simplicity I made a 100 inch x 100 inch panel at 100dpi. On a new layer, choose Edit>Fill>Pattern and select the pattern you created. It will be the last pattern in the list of patterns that pops up. The result should look like my example below. Add colors, textures and whatever other effects you want... or just leave it clean and simple. Good luck.
