I helped my dad build a 3 bedroom house out in the country and it took us almost 3 years from start to finish with us doing all the work including the plumbing, electricity etc.
We bought already made rafters to save a bit of time and rented some equipment to lift up the rafters and walls as well as dig the basement out etc.
We did have a concrete company come out though and pour the concrete for the foundation and basement but we did all the rebar etc.
Most home builders though that build homes all the time could build a home in around a year to a year and a half.
You'll certainly need some help with building the house but once the walls are up and the foundation is poured you can do most things yourself after that.
Building that house with my dad was fun and he's still living in it but I would not want to go through that again because it took so long.
I would rather just hire a home builder to build the home especially a three bedroom home and have it put up faster.