Alert when structure built within radar coverage.

Can we get an alert when someone starts building something inside an area covered by Radar?
I just got stomped because my opponent was able to get a TP built and units through before either myself or team mate noticed (we were viewing other planets).

No, because you're not supposed to be able to tell what the radar blips are, that's what scouting is for.

So make it generic.
I've not scouted it so I don't know what it is, but I could get an alert that says 'enemy structure under construction', similar to the 'enemy detected' alert.
Obvious issue is that this would be going off all the time on smaller planets with active enemy forces. So either make it time based: if last time new structure detected > 2mins then alert if new structure detected, something like that.

OR

Can we get an alert when an enemy orbital fabricator arrives in orbit perhaps?

This comes down to planet management and is something the game currently makes too hard for players to effectively manage. Ideally we'd need 2xPIPs per planet in a system (front & back) and alerts for celestial unit movement.
Oooh, can I have the system view in a PIP, that might solve some of it.. but really we're just fighting the lack of minimaps for useful things.

With the addition of the unit cannon, and the ability for enemies to effectively appear 'anywhere' on a planet with little to no warning something should be done to at least give the player a chance to organise a defence - you don't know where the units will arrive, but you know they're coming.. it's better than the nothing we have at the moment..?

But how would you even know just from radar that it is a structure?

radar isn't supposed to tell you what's there, only that something is there. If you see a bunch of radar blips, you're supposed to scout it out and figure out what's there - otherwise the enemy can draw your attention with a blob of land scouts as a diversion, it looks the same on radar as a large army.

speaking of, I'd like to see radar stealthing units.

What if you place a radar outside someone's base and they start building stuff