If you're planning on building an ADU or JADU 'yourself', my suggestion is to make sure you have some previous knowledge of construction and also make sure you know good sub-contractors in the following trades:  electrical, plumbing, foundation, roofing, framing, drywall/paint, stucco, tile, cabinetry, flooring, HVAC, concrete, etc.The last thing you want is poor quality work that has to be re-done because a handyman or the wrong tradesman did the work.

Unless you are doing all of the maintenance yourself, figure about 5k yearly for touching up paint, repairing misc. items the guests break, bikes, kayaks, BBQ grill, pool maintenance, lawn service, pest control, replace TV remotes every time someone checks out. 

Blue tarp on the roof, lots of trash in the front yard, and it's very apparent that the house has not been washed or painted in years. 

Hard wood stairs, LVP flooring throughout, completely painted.

Purchase price: $300,000 Cash invested: $80,000 Let me paint a picture for you of this amazing cabin we've got in the Red River Gorge.

I also really enjoy the process of taking something old or rundown, and making it new again, I just love seeing the results even if it's just a fresh coat of paint.

Paint, flooring, and upgrades.

Plus the holding costs and permit costs if it’s more than paint/carpet.

You'll do this for everything in the home that requires replacement: interior paint (4 years), flooring (12 years if you use 12 mil LVP), roof (20 years), hot water heater (10 years), oven, washer, dryer, garbage disposal, microwave and so on. 

Spending $20k on exterior if windows roof and painting are needed will eat up costs pretty fastBest to itemize what needs to be done and then determine a rough estimated cost