You can spawn the construction model on them, but the final animation step has to exist in the model, or its absence has to be hidden behind additional effects.
For Terran you should probably just make the regular unit model rise out of the ground shortly before completion, like how structures do it. In fact I think Terran structures don't have any birth animations at all, just the retracting scaffolding, which is part of the build model you can add to anything. The Thor also has some unique models but I think they're outdated.
For Protoss you can use the warp-in animations where they exist (all Gateway and Stargate units plus the Immortal, possibly the Collossus is the only exception) or apply the decloaking effect, or just mess with opacity and tint color. Maybe add some lightning or the Warpgate warp-in model to make it look cooler.
For Zerg the ground units have an Unburrow animation you can use while they "emerge" from the cocoon and the Larva-morphed flyers have a birth animation suited to a grounded egg, things like Broodlords might require playing with their height. You obviously have enough eggs, cocoons and building bubbles to use for the main construction phase.
Kabelkorven AuthorIs it possible to add some kind of animation for a SCV that builds a Siege tank? (As if it placed it as a building on the ground)
Is it possible to do the same for Drones building a Queen?
Or a Probe build a Colossus?
Anyway to make this look good?
Or shall I just scrap this idea ^^