Same here. Can´t build new Unimatrix in another system

If you check your traditions you'll see that some of them increase your unimatrix building cap.

I'll have a think about how better to show this in-game. The Megastructure interface isn't great for that.

I believe you need enough mass like 2 or 3 planets in system also try to build when constructor is in the system you want to build in doesnt show when outside system