Hi Michael, We own and manage a 4 unit, plus a commercial garage we use for storage and two yards for our tenants.
The biggest major expenses in an old building( ours was built in 1893) is the roof( $15,000) The furnace $500 each time they come out, pumps burn out. Each time you have a tenant leave there is repainting to do either yourself or hire it out($200) If they put holes in the wall or were slobs throw in another $125 for cleaning, another $60 for hole patching depending on the size. Doors get punched a lot when people rent, your going to replace some of those, you will spend a lot of time in Lowes or Home Depot.
Spruce up your outside property with new paint on a fence, plant perrennial flowers, and replace bad grass with sod and water water water. Plan on a higher water bill your first year.
Of course these expenses can be reduced if you do the work yourself. I assume you have good windows or count on $500 per window for the good ones with lifetime warranty.
Also, plan on repairing water damage in an old building, water will be your worst enemy.
make sure you tell tenants to take out their garbage regularly and make them responsible for keeping the place clean.
We pay their utilities and cable to compete in our market. We have maybe a week between tenants because of this deal.
Advertise on Craigslist for new tenants. raise rents to improve NOI but more importantly to attract better quality tenants.
All the above will be expenses to consider when budgetig time and money. Do this for one year and keep track of expenses as they will fluctuate over the months, they will not be consistent until you've done this awhile, but really each tenant brings their own expenses. Get and keep good tenants,
Price toilet parts out, you'll replace those too.
Get the tenants a gas grill. They appreciate the little things in any market.