In the traditional world, the chassis and enclosure are related but
separate items. The common technique is:

1. Electronics built on aluminum chassis box. Available
pre-fabricated from Hammond etc. Or make your own from sheet metal.

2. Front panel bolted to the chassis box. Knobs and switches and
meters go on the front panel. And are either wired to the stuff inside
the chassis or control variable caps etc. on the chassis via long
shafts. Front panel for a big project is often 19" wide rack-mount
panel (again a standard size available from Hammond et al.)

3. Enclosure is a sheet metal box that slides on from behind. Made
using sheet metal tools.

At the high end, "sheet metal tools" are a big shear for cutting and a
brake for bending. At the low end you make you own brake out of 2x4's
and hinges, and cut with hacksaw/table saw/aircraft snips (depending on
type of cut, thickness, and material.)

For the really classy look all the holes you need can be cut with
punches. More likely for a hobbyist is drills and hacksaws and files
and the most valuable tool of all: the nibbler.

Tim.