Read the following article and hopefully it'll give you some guidance: https://www.biggerpockets.com/member-blogs/10850/85351-nothing-will-work-until-you-do-maya-angelou2) it sounds like you a ready have some foundation, but the best investors never stop learning.

I've loved living here and they've done a ton of work to bring it up to snuff (including replacing most of the foundation).

Not to mention, consideration of the age of the property and condition of the foundation.

The condition report stated the owner did not know of any defects in the basement or foundation but the tenant mentioned they did not use the basement because the current owner told them the basement gets wet when it rains.

Here I have seen major items such as leaking pools and foundation problems so as an agent I can inform my buyers of what I know and they can make an informed choice.

Going to build an ADU (800 total square feet) next to a house that has a basement and a second floor.Question is, which costs more:1) Building a second floor (roughly 400 sqft foundation and 400 sqft second floor).Or2) Build a basement (roughly 400 and 400 again).I realize there are many factors (sewer slope in basement, soil removal, etc.), I was just curious about general cost (2nd floor wood vs basement concrete).Any thoughts on the matter are greatly appreciated!

@Jonathan Bombaci ​There is more to foundation repairs than just the foundation.

I have not added an attached garage, but am adding  a stand alone garage to one of my properties.I think that a stand alone garage is better because by attaching the garage the garage and house will settle differently, possibly causing foundation issues in the future.

Finding someone with experience catching larger projected expenses (foundation, rotting frame, etc) will be invaluable.Also, always looking to connect with investors in the area and see what I can do to help out as well.

As it is all inspected at each level from foundation to framing, electrical, insulation, and completion.