There are actually a lot of threads about this. From what I've read, most DIY paint jobs aren't going to be durable, and you'll be recommended to use etching primer, depending on the frame material.
If you do spray paint the frame, your "totally custom" paint job will be chipped, scratched, scraped, and otherwise torn up in no time especially if you ride off road or through any sort of debris.
Most people recommend powder coating or at least a professional paint job, and making sure you find someone who knows what they're doing with a bicycle frame and fork.