Price per sq ft on new build home(custom build)/ how to cover my arse

Are you factoring in the cost of the land in your sq/ft price or do you already have the land?

That’s also going to depend on the house? Are you planning on building a separate suite or structure for you and wife?

Don’t have the land yet either

It depends....$160/sq ft, without doing crazy lavish finishes but using better than builder grade flooring and fixtures, should be ballpark.

I love the idea of a multi generational home...here are a few common sense suggestions to consider:
--universal design: be looking at single-floor plans, with all doorways wide enough to allow for a wheelchair. It's not expensive to do this, and it means you won't have to retrofit things in 20 years.
--walk-in or roll-in showers in at least one bathroom, with enough floor space to turn a wheelchair and accomodate another person to assist with bathing. Flexible shower curtains on a rail over fixed glass doors (maybe not everywhere, but in at least one bathroom)
--handrails at all exterior entry doors, or at least on the most commonly used family entry
--closet space: whether lining hallways, near the garage entry, or extra large closets in all bedrooms, multiple generations means lots of STUFF. An excellent way to keep the peace is by having a place for everything.


Also think hard about ownership: is the house going to be a jointly owned asset, or will you gift your stepdaughter with downpayment money and then pay a fixed amount toward rent/utilities/maintenance? Or are you and your wife funding the build and then leaving the house to her daughter? You need to consider all of the implications of joint ownership in detail before you go all it. Will the house have a mortgage?

It can be a completely cordial relationship and still become a complicated mess for reasons beyond your control (death, job loss, dementia, etc). Thinking about various scenarios and planning for them help to keep things cordial.

Finally, don't overbuild for your area or neighborhood. Dual master's suites may serve your purposes, but if you stick the house in an area of 3 BR starter homes, you aren't making a smart investment.

Obviously need to consider how long your family intends to live in the home. What if son in law needs to take a job in another city due to layoffs or less opportunities at his company? Large homes in general sell for less per square foot than smaller homes. A customized home may be even more difficult to sell. We recently helped my in-laws purchase a home just down the street from us using a reverse mortgage purchase. They bought a $275K house and only had to pay down $110K. There are no payments as long as they occupy the house. All interest rolls over to the principle owed. They are also guaranteed to never owe more than the house value. In other words, if they both pass away and the loan balance is $350K and the house worth $325K, no money is owed if house is sold for the value. If house is worth $375K in that situation, house would be sold and estate would get $25K.

My wife is already in a wheelchair do to brain injury. This is a big factor of why we are doing this. Shower and wheelchair specs throughout our house have already been considered

We built a house similar to what you are talking about in 2013. It was on inherited family land so purchasing was not an issue.
My mil lives with us. She is not married and my wife is an only child so it was a no brainer.
The house we built is all under 1 roof but functions as 2 separate houses with the exception of the laundry. We share that.
The MIL apt is around 800 square feet with a good size BR and a bath with walk in tub. She has her own full kitchen, central AC, water heater and direct tv setup. She uses our WiFi She also has her own carport. I know costs are out of whack since it was 7 years ago but it was cheaper doing that doing a same size separate home. We did ALOT of work on the house ourselves and ended up in the low 100 per ft living. My wife and I acted as the GC. Remember the land was not figured into this number so yours will be different.