@Tove Fox hope you find this copy & paste useful:)-------------------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

@Polat CaglayanI've never seen a formula but here is a general rule of thumb for multifamily:The class of an apartment refers to the quality of the building, which can be determined by a number of factors, including age, location, and condition: Class A: These are the highest quality apartments, typically built within the last 15 years.

-------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

-------------------------------------------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

The loan amount will typically be determined by appraisal (LTV - loan to value ratio) - but your qualification will also be based on other metrics like you mentioned - DSCR ratio, FICO and some other factors. 

Issues 1) even garage conversion ADUs in single family zoned areas typically cost more to build than the value that they add.  

So, a house that would typically cost $100 per sq. ft. to build 5 years ago, is now costing $200 per sq. ft. 

Most DSCR loans come with a prepayment penalty that is typically 5% for the first year, 4 points for the second, 3, 2, or 1 pts for each year.

@Matthew Drouin had a great reply:"Typically 50% of revenue is going to go right to operating expenses on small multi family. 

How much upfront costs are typically involved in a project before you know if it's a viable project to pursue?