How Far apart for Rafters (Patio)?

I am building a 12x17 patio cover which I am going to run right off the flat roof. I'm going to use 3 4x4 supports which will be bricked to the top. I plan on using 2x6 rafters. How far apart do I need to space them? I'm going to put recessed lights and a ceiling fan in and use a hardi soffett. Thanks... show more I am building a 12x17 patio cover which I am going to run right off the flat roof. I'm going to use 3 4x4 supports which will be bricked to the top. I plan on using 2x6 rafters. How far apart do I need to space them? I'm going to put recessed lights and a ceiling fan in and use a hardi soffett.

Thanks for the help.
Update: No snow, live in Houston
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