Dear Flatlander: the laylights in buildings constructed before the advent of electric lights have a pleasant aesthetic effect. But for new buildings they would be impractical.
As for titanium, don't knock it. Until now it has not been much used in buildings, because it is expensive, and has fabrication limitations. But a short time ago there was an article in New Scientist about a new refining process which could reduce price allegedly by as much as seventy five percent. That could greatly increase its use.. I wonder if it can readily be made into doors and window frames.Most likely use would be for roofs, because it is light and corrosion resistant.