You may also want to account for some expense for reserves (3-5%) as most folks start saving some so when the roof, boiler/heater goes and you need to replace it there are funds to help pay for it.

To me it’s a good method to grow quicker instead of the steady CF on a monthly basis  IF you're selling it, then replace it with another property that cash flows higher, you're cash flow is higher, and your property value increases, with the same equity.

Heavy contamination usually requires replacement or a lot of cleaning.

The issue is that the house is a single family 2bed/2baths built in 1982, roof has not being replaced.

This is how I renovated a duplex in 2020 with only $6,000 (entire 2800sqft interior painting, refinished/re-faced two kitchens and replaced all appliances in each with used/like-new appliances, new sinks, new tile backsplashes, new hardware, new sinks/faucet, 25% flooring replaced, and one bathroom (everything but the shower which was fine as-is).

HML's will want a first lien position, so if you have financing in place already you need to look at a refi that gives you the extra capital you need to pay for the rehab while replacing the original loan. 

Upgraded the bathroom, kitchen, some appliances, built a laundry room, replaced cabinet hardware, replaced damaged flooring tiles.What was the outcome?

The other option is that he continues to pay rent until a suitable tenant can be found to replace him (or the lease would normally expire).What does his lease say regarding this issue?

My area it is $6 sf to replace. $6000/10 year life span/12 months= $50 per month for just the one item.

Paint or marker on brand new carpets, attempt cleaning and if stain persists, charge for replacement minus prorated life.