building a custom made 4 foot level

Cause there's so many options available to buy one inexpensive

Most manufacturers sell replacement parts for broken levels. Seems if you could bed them nice and square/level/plumb you could make a level. How level it would be would depend on how well you got the vials bedded.

Stanley

http://www.stanleytoolparts.com/levels-vials.html

I would assume for the long edges you could use some sort of metal channel. For the wood you could make a laminate of your choosing. For parts you could buy a cheap level and remove its glass and bubbles. That should be all there is to it. Like the first person stated though, it's probably cheaper to buy a quality level than build one. Finding a old one and restoring it is another option. Best of luck though. Really wouldn't be a bad project if you don't mind spending the money

Here's one that looks nice and is American made

https://www.amazon.com/10136-48-Laminated-Wood-Level/dp/B00176LF96/ref=mp_s_a_1_10?crid=8I7DWFZ31UI7&keywords=wood+carpenter+level&qid=1650084519&sprefix=wood+carpenters+level%2Caps%2C63&sr=8-10

because it makes no sense probably.it's a precision tool that if it's not perfect it's worthless. good luck with it.

I sort-of like the idea, if for no other reasons than the challenge and making something that is both functional and beautiful. I would lean towards the lamination and then using the jointer (hopefully with a long bed) to get you that one perfect edge, working from there to square everything up. And if you need another level to make sure yours is level when embedding the vial, use a water level with the ends of the water level at each end of your level.