420 sg ft harage need hvac split unit sized so i can get permit issued

I have a 420 sq ft garage that I need to fit an HVAC split unit into, so I can get a permit issued. The size of the garage is 300-500 sq ft. I do have a preferred brand of HVAC unit, size appropriately to the size of the garage, and the brand is Other (please specify). I am looking for professionals with the expertise to help me get the right sized unit according to the size of my garage so I can get the permit required for the installation. If you have the experience and know-how to help me with this project, please reach out. I look forward to hearing from you soon. Thank you!