I can help
Do you have any kind of sketch you could draw and share with me?
I want to make sure I fully understand your configuration.
What city and state do you live in for possible snow load consideration?
On the zoning question, this would not be considered a principle structure, it would be considered an accessory structure. Some Zoning Codes have different setback requirements for the two different types of structures. You will either have to see if the Zoning Code is online for the jurisdiction you are in, or you will need to call them and ask that question about the setback requirements. My advice would be to call them 1st. A phone call is free and you want to make sure you are not assuming something that is incorrect.
Let me know about your city and state and I can help you on the rest of the question.
I’d like to point out that a Professional Engineer’s standard of care typically includes a site visit to assess field conditions and get an overall understanding of the structure. This can obviously not be accomplished through the internet. The information provided here is meant for planning purposes only (general sizing and budgeting) and is based on the information provided by you. All loading cases considered are for vertical loads only, no lateral analysis has been completed. The information should be verified by a professional engineer who can visit the site to ensure that potentially important information has not been overlooked or omitted.
For your 16' span ridge beam, you could use the following:
4x12 or 6x10 Douglas Fir (#1 grade beam)
For your two 16' span side beams that your rafter tails rest on, you could use the following:
4x10 or 6x8 Douglas Fir (#1 grade beam)
For your two 16' span gable end beams that your post supporting your ridge beam rest on, you could use the following:
To make your structure look symmetric, I would use four 6"x6" Douglas Fir posts
And also use the 6x members for the various beams I sized above.
You can use Simpson Strong Tie post bases, see below:
You will need to have a local engineer detail your connections, determine foundation requirements and check the lateral stability of your structure.
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