Iron houses

If humans are to live on Mars, there must be a way to build things.  It so happens that there may be abundant iron on Mars.  As a matter of fact, Mars gets its red coloring from rust.  Don't know if that would make Iron Man happy, but it could be useful.

With its abundant carbon dioxide, Martian iron can be obtained.  An energy source would be required.  A space modulator would not be.  Perhaps concentrated solar power could do it, but if not, then nuclear energy could be used.

Given the massive amounts of energy required for such a process, perhaps there could be better ideas than this.  At any rate, large amounts of iron could be available.  If not feasible, nor desirable for complete enclosure of a habitat, then perhaps a structural skeleton could be built using iron.

Iron would not be much use for export to Earth.  But you wouldn't have to import the stuff.  That's a relief.

It may be possible to make glass on Mars as well.  If so, structures could be made that could admit light, which would enable some agriculture.  If not glass, a transparent plastic may be possible, or even more likely.

At any rate, it is theoretically possible.  With an appropriate means of getting there, colonization is not out of the question.