How do you even go about building a bike? How many parts do you need to buy? How long does it take? How do people plan it? And what are those bikes built in a shed like compared to the stuff you buy from the shop in terms of performance and how smooth it rides?
A frame
headset
front fork
wheels, rim tape, tubes, tyres
gear levers, cables (inner and outer), derailleurs
brake levers, hoses or cables depending on if hydraulic, calipers (and disc rotor if disc brake).
Cassette , bottom bracket, Crankset, pedals, chain
saddle, seat tube
Handlebars, bar tape, stem.
Then optional stuff like mudguards. Gears can of course also be optional.
When I was about 12 years old my dad got me a bike frame and fork from the dump. I cleaned up the frame and fork and then painted them with a tin of humbrol paint. I turned it into a tracker bike with cow horn handlebars and knobbly tyre etc. So quite early on I got used to fitting stuff to build a bike.
In late 2013 I learnt to build wheels. Since then any new bike I’ve got the frame and then build the wheels. A wheel is a hub, spokes, spoke nipples, rim. Plus some grease for spoke threads. That’s it.
My recumbent I had to import as not sold in UK. So I imported the frameset and then built it with components I already had plus built some new wheels for it.
Bikes are mostly about bolting or screwing things in place. Adjusting , such as derailleurs. As long as you show some mechanical sympathy and know when to take a break from a build as you’re tired or making mistakes; it’s a very satisfying thing to do. You’re never under pressure time wise, so if you’ve got the wrong component, you can return it, order the right one, then continue build when it arrives. I learnt to assemble hydraulics from scratch last year. With modern frames you have integrated or semi integrated headsets so no special skills required, they just drop in place. Just make sure headset is right way up.
You end up with a bike having exactly the components you want. You know exactly how it fits together and was built. It gives great confidence on the road should something need repair.