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1. So you have 2x8's spaced at 12" o.c.?
2. What is the height of your framed in wall on your cantilever?
3. How will your ne roof be framed into your existing roof?
4. What city and state are you in for possible snow load?
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.
Your cantilever of 28" it too far. Most designs limit a cantilever like that to 24" as the absolute maximum. You could possibly sister an additional 2x8 next to each existing 2x8. I would use a 6' long 2x8 as the new sistered member and you will need to through bolt these together with 1/2" diameter through bolts spaced evenly along the joists.
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