Hello,
The actual system showing in green where you can build works fine if you don't have anything build but it is a pain every time i want to place a new building which is not the classic 2x2.
Lets take an example of an Improved watermill (Christmas is coming). I get a new one and since it has a production cycle of 1 min I want to place it as close to a storehouse as possible. But of course all the best spots are taken. Now i have to start moving 2x2 buildings around just to notice that there is actually a tree or something I couldn't see which allows 2x2 buildings to be placed but not 2x3. So I move my 2x2 building back and start moving some other buildings just to see that the entry/exit point of the imp watermill is actually sightly to the left side. So i place the 2x2 buildings i moved back and start looking for an other spot....
There should, in my opinion, be a way to see if you can place a new building without having to move all your buildings away. Something like display the building in grey if it could be placed instead of the green/black and show the building (or buildings) which is blocking in red or something like that. A building mode where you could move every thing around and then accept if you are happy or cancel if you don't like it would be an other solution. The only viable method at the moment is to build your island on the test server and try it out....