Help with DIY Building Permit / Engineer Stamp

Does anyone have a recommendation to get engineered drawings for a simple patio cover?

I am planning to build a small & simple patio cover for my house within the Houston city limits. I talked with the permitting center and got an example set of plans to use as a reference. Since their plan would not work for my house I made a minor change (which appears to follow code) and applied for the permit. Now they rejected it and said I would have to use their exact plans or get an engineers seal.