Disaster Building
I unlocked the Disaster Building yesterday (90,000 population and $40,000 coins). It takes 12 hours to complete bulding after you start the build, so plan accordingly.
Once it is complete, you see a little tornado icon at the building when you can start a disaster mission. Dr. Vu will say something like "I made contact with aliens", or my earthquake machine worked well on the ant farm, should I try it on the city?' or he mentions his new meteor machine. If you have the items needed (gloves, battery and transmittier) and choose to start a mission, there is an animation of whatever disaster he mentioned hitting your city.
My first one was the aliens, who came down in their UFO and destroyed 1 building. Your population drops as no one can live in a destroyed building. You then get the little upgrade icon which shows you the items needed to rebuild, as well as the number of keys you will get for rebuilding. It is somewhat like the items needed to upgrade your regular buildings, but seems to be a bit heavier on the total items needed. Once you have all the items, you drag them to the destroyed building, just like upgrading. It only takes 1 "upgrade to rebuld the building completely.Repeat for any other buildings which were destroyed.
Once you have fixed all the buildings destroyed, you can immediately begin a new mission.
Just FYI, my second mission was an earthquake that leveled 4 buildings and took me several hours to collect the needed items to rebuild. Thrid mission was the aliens again, only this time they took out 5 buildings. However, 3 of the 5 were easy to repair. Fourth mission was another earthquake, but the animation was meteors hitting the city. Only 1 building destroyed. Fifth was aliens again, but again only 1 building. Next up is the meteor machine, but I haven't started it yet as I am building up reserves before he knocks my buildings down again😕mileyhappy: The missions don't seem to be progressively harder, it is just random luck I guess.
The damaged buildings do not affect your Happiness meter at all; the only downside is the loss of population, and therefore, coins per hour coming into city hall. If you can live with a few less coins per hour, you don't have to kill yourself trying to gather the items you need in the Global Marketplace, just build them yourself.
The rebuilds have so far given me from 1-3 gold keys per building, and seem to be dependent on how difficult the rebuilding items are to make. You get more keys for a building where you needed chairs and grass then for one which you can rebuild with wood and a hammer.
Of course, the keys don't help you at all unless you have built the Education or Transportation buildings, which unlock the buildings which can be built using keys.