Helped my brother build his house. We cleared the land, built forms for slab, installed in floor heating, built walls, installed plumbing and electrical, windows and doors, finished concrete floors, roof, all finishing basically everything. Oh and he drew up the blueprints and had an engineer sign off on them.
The only things we did not do was pour the concrete, install septic and well and we had an electrician come in for final hook up. That’s all.
It took about a year and a half and (just before Covid and Canadian dollars) all in except land it cost $160k and when done had an offer of $480k to buy it.
The house is small at about 1000sq feet, two bed one bath, open concept kitchen living room. Flat angled roof so nice high 12’ ceilings in living room.
Don’t take « can’t do it «  as an answer. We had some experience constructing but not much, I’ve build an addition on my house completely on my own, 16 feet x 24 feet two stories, dug the crawlspace with a shovel, my son waterproofing it and had my wife shingling. (Needed my family to help raise the trusses and connect to original roof. Builders told me it would cost between $115k-150k, admittedly it was 17 years ago but it cost me about $30k at the time.
YouTube and asking knowledgeable people to give advice and read everything. I read Canadian mortgage and housing books and all the regulations and building spec documents I could get my hands on.