Can anyone give me an idea on how i could make vehicles like in banjoo kazooie nuts & bolts and then make it all driveable?
Yes 
You model the vehicle in a 3D software like Maya, 3ds Max, Blender,…
then you watch a tutorial, e.i.
See that doesn’t really help because im looking for modular building not premade vehicles for example
https://www.youtube.com/watch?v=5e-4G4nEV_4
that should’t make any difference.
This explains to you how to setup car physics in Unity.
If you want to make an interface for the player to change or build a car, you build that around your car physics. Changing a part just adjusts some variables in the physics.