Its extremely important when running tighter margins like what you're talking about to focus on age of HVAC, water heater, appliances, roof, etc.

Because the cost of roofs, ac units, water heaters and so on don’t care if you collect $600/mo in rent or $3,000/mo.  

I also invested in improvements: new roof, water heaters, other major appliances, and a kitchen renovation.Now, my situation has completely shifted.

Maybe have a decent sized pool of cash to take care of the occasional roof repair or personal expense, but almost entirely in real estate?

This is especially true the more people you try to cram under one roof. 

., HVAC or roof replacements)?

Although instead of knowing about roofs and rehab.. land folks need to know about:Zoningwhere is the power  is there internethow deep are the wells or is its an area that water is super toughDoes it perc. and or how expensive are septic systems.Wetlands Etc.Now if you target land with all city services then its just dead simple.. figure out the retail value and buy below it and do your flip..

-Spreading costs: One sewer line, one roof, etc.

Can I demolish the roof and build above it to raise the living space above the base flood elevation.

What kind of roof is best for your area?