We have in a hand the permit to build a 3/2 1100 SF home in backyard.

Finally secured builer in October 2023 took until jJune to get permits and now The insurance company says they won't pay until building is complete.

I have seen it from the street and it "could be" 2/1 1606 but won't know for sure until I can get in which won't be until next week.Question is, wondering if it's possible the owner added on but did not get a permit so it's not on public record. 

My permit cost the same as SFR.

You'll either have to convert the house into a legal duplex by getting permits from the city or you install an electrical panel split so that you can track each units/bedrooms of their power usage.In terms of lending world and being to use the rental income, the property needs to be a legal duplex meaning title must be shown as a multifamily and not a single family in order to use the rental income separately.

It could be permits or some issue with the contractors which could all add to your holding costs.

Does anyone have an idea of the who I could hire to make drawings to submit for a permit?

Keep in mind that you would have to get permits and such for a project like that. 

This figure includes the construction of the building but excludes land acquisition, permits, and other associated costs.Cost per Door (Unit)The cost per door, or per unit, in affordable housing projects can also vary widely based on the specifics of the project.Average Cost per Unit: Recent affordable apartment buildings built using public funds, such as Metro housing bond dollars, have cost between $412,000 and $522,000 per unit.

We really can't tell you anything based on the information offered, it depends on local laws, costs, rents, materials, permits, etc.....