energy to matter building

[Deantwo]

was thinking of something like producing low stuff like metal and gems with out the need of the stuff on the planet as a late game kind of thing

If it is a late-game thing, you already have access to all those things in great quantity and better quality.

Unless the building create very high quality commodities, it would be useless. But at the same time if it create commodities that are too high quality there will be no need to make anything else.

And like I mentioned earlier, cities have infinite resources and therefore infinite electrical power.