@ NeiljohnUK:
-Thanks for your encouraging remarks, even though I didn't do any CAD or even a drawing beforehand!

These extrusions aren't by themselves really that structurally sound for the job,
as the Make-up table (liberated from a TV production company estate) was initially rather flimsy:
The castors are bolted thru reinforced corner steel gussets, providing sturdy bases for the horizontal beams,
which are locked by smallish anchor bolts with mere eccentrics for holding power.
I figure they're really for making store counters and the like, not carrying 300 lbs of metal.

Then the tight-fitting lacquered MDF bords provide both the cross-bracing and load-bearing with the top horizontals.
Tabletop rests on top horizontals and verticals, piano hinged drop-leaves supported to side MDFs.
Drawer cabinets sits on bottom blockboard supported by the corner gussets and lower horisontals' flanges.
I wouldn't have tried doing it freehand, I needed the wood shop as well as the metal shop at work to get everything square and tight.
Most time-consuming was the cutting and fitting of extrusions and panels into the 5-sided rigid box.