You need 10 epics of a color to unlock one of the buildings.
All my goals passed except the Garden of light
Garden of light- Need 10 white Epic Dragons
Eternal Flame- Need 10 Fire Epic Dragons
Flower egg- I think it was 10 Green Epic Dragons
Sunshine Templeplanetary Tower- 10 Epic- purple
Pantheon Pool-I think 10 water Dragons?
So for each locked building, you will need 10 Epic Dragons of a certain color.