Do you know of a pen-and-paper RPG with a good construction mechanic?

First, I am look for pen-and-paper style RPGs, not video games, so please don't recommend those.

What I am interested in is an RPG with an interesting way to build things. Particularly spaceships, mecha (giant robots), or other vehicles, but interesting character building would also be appreciated.

This is the list of systems I am already aware of, and don't need recommended again:

And because most of these games have multiple settings, be aware that when I mention one I am referring to every edition of that game.

GURPS

Pathfinder

Dungeons and Dragons

Eclipse Phase

Mekton Zeta

Cyperpunk and Cybergeneration

Shadowrun

Any system by White Wolf

All the various Palladium systems

Mutants and Masterminds

Hero System

d20 Modern (and Future)

Any Star Wars setting

Any Star Trek setting

Babylon 5

Traveler

Battletech

Fantasy Craft

Spy Craft

The various Guardians of Order systems

Alpha Omega

Chronicles of the Void