20x30 1.5 story, porch roof question

[ntexastomm]

New to the forum. Planning to start framing in Sept. and I have questions. Background, I'm building a 20x30  1.5 story with wrap around porch on 20' south (6') and 30' west side (8'). I have power to the site, rough plumbing and concrete slab done, Septic done, just finished installing a 1200 gal rain water tank underground. I want to have the gutters from the main roof supply the rain tank so I cant tie the porch roof directly to the main roof. This also will make the porch roof pretty flat. Anybody done anything similar or have advice.

Note: the "I'm building" quote is a stretch, I'm the chief drawing jockey and will direct subs for framing and roof but I hope to complete siding and most interior work.