Something i did recently to help with collecting coins from builds for missions that works for me. Probably not the best, it’s certainly not gonna make you rich but it can help with knocking out the (coins from buildings) missions with out much effort.
I don’t like to have to baby sit the game and be collecting coins every couple hours especially from buildings, so i made a 9x9 area of maintenance facilities on the second island out of the way. They are fairly cheap at 47,500 coins a pop, take up little space each, have a fairly high cap for buildings 8820 and the time to max is long 21 hr. Put a collection tower in the middle gives you 80 buildings to collect from. 3,800,000 coins for 80 buildings. With no decorations they will give you 705,000 with 1 click every 21 hours or around once a day. If you have coins to spare and put decorations around you can boost that up over 1million which you will probably have to do as most of the (collect coins from buildings) missions also have a % requirement.
This with my other buildings and most collection missions don’t take more than a day and a half.
If you routinely get on the game you could opt for a different building that maxes quicker but even so the max production on most of the small buildings with quicker max times are pretty low, so even collecting them fairly frequently you probably won’t end up with a whole lot more coins than with my method unless you are waking up every few hours to collect at night as well lol. Those buildings are a little cheaper though if that is an issue.