Usually an independent structural engineer (see also retired from big firm and still doing small stuff) will provide you a 18x24 sheet with a small plan, details, elevation, section for a fee. Usually $500 a sheet or close to that.
Helps to know a few contractors, architects, engineers, inspectors in your area to find that person.
But they will likely double the cost of the build because they will take it from 6x6 posts to 8x8 posts and want 2x8 on 15" centers...etc
Just a sample
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