Are you looking for a dollar amount or percentage? 

I'd offer either a lower percentage or a flat fee.

Some do total debt bids if there is equity, some do a percentage of fair market value if there is not enough or no equity.

Maintenance and cap expense is sometimes forecast as a percentage of the rent but it is much more a function of things like number of kitchens and bathrooms, square footage, quality of tenant, etc.

I believe the city will require you to designate a number or percentage of the new units as affordable (RSO). 

The meters will tell you what percentage of  the boiler's total heat (actually percentage of the heated fluid) that each property uses.   

The Solo 401(k) also has the advantage of being more favorable for real estate investments using debt-financing such as a mortgage - as the 401(k) is exempted from a small tax called UDFI that an IRA would pay on the percentage of income derived from the borrowed money.If your intention is to have the retirement plan invest in leveraged rental property, I can pretty much guarantee you will find either of the checkbook plans to be much better tools.If you have qualification for the Solo 401(k), the exemption from UDFI on a leveraged property investment will be a nice benefit. 

Only buy it if you can get percentage rent from your drug dealer tenants.Obviously joking, don't buy it.

For instance, is it a percentage of the total loan? 

@Elijah VanDenBerg, as a percentage of rent for repairs and CapEx, I wouldn't discount too much.