There is a "Construction" actor that seems to be related, but I'm still working on how it actually does its thing. It triggers the animations when a "Build" ability is used. I'll get back to you as I learn more.
One way I did it was to create an ability of type "Effect Target".
I had this ability have a "Launch Missile" effect which on impact triggered a "Create Persistent" effect.
Still with me?
For this last effect ("Create Persistent") I had the "Periodic Effects" field point to a "Create Unit" effect.
I also set the "Search - Reveal Flags" and "Search - Reveal Radius" fields on the persistent effect to "Unfog" and "5" respectively.
It was a whole lot more complicated than that, but it's a general idea, I hope it's kind-a helpful anyway.
Thanks! That solved MY issue. The ability is called "Build in Progress", but I bet that's what you meant. I was trying to make a Marine build a Viking. The Viking would show up and be controllable immediately without the 5 sec timer I had set for it. A quick peek at the abilities on the Viking and that was it. Thanks again!