Detached ADU - Determining Development Costs? - Portland, Oregon

[Steve Green]

Hi Everyone,

My first post here - I have been reading and studying the great resources on this site and learning a ton.  I have a single family rental in Portland that is cash flow positive, but not by a lot.  I ran it as a VRBO for a couple years and did well, but as my career got more intense I switched to longterm rental.

I'm researching adding a detached ADU to the lot to boost my returns. My livable square footage is about 1,800sf so that puts me at the limit of 800sf for the detached ADU assuming I am reading the code correctly. So I have several questions and I'm hoping the experts here can point me towards some good resources:

1. What are typical development costs for a detached ADU (permits, etc.)? Any good websites that show examples/typicals on these?
2. Where can I find a list of all costs to execute a detached ADU so that I can avoid surprises and overruns?
3. Anyone have a slick proforma excel document for a detached ADU?
4. I like the idea of container homes because of the "turnkey" nature and the fact that I could remove it at some future date to another site (or sell it) if/when I wanted to develop the lot to multifamily (which it is zoned for).  Are these allowed in Portland?  Anyone had any experience with these?
5. Any advice on configurations (# bedrooms/baths) to maximize returns?

Thanks in advance for your help everyone!

Regards,

SG