Even though the FAQs does give general idea of where those are, as well as SCANNING on the map does show basic area, I still had a helluva time trying to locate allot of these golden doors. Then I figured out something pretty easy.
In FREE PLAY MODE, use your map to scan and place MARKER by the "arch" icon of choice, which represents a GOLDEN CHARACTER DOOR. Now allot of these are not easily found and you can waste HOURS trying to search every crevice for them. So here is what I discovered by accident.
In MOST cases where ever the GOLDEN DOOR is, there will be a corresponding GOLDEN BRICK you can get. If you actually follow the path up the side of the building using the character / suit needed to get it, then you will end up hitting that door just by following the path. So recommendation is: 1. Locate GOLDEN DOOR of choice and mark it. 2. Fly up to the closest GOLDEN BRICK location to determine power / character / suit needed. 3. Start flying down the building towards ground and on the way look for the DOOR. 4. If you dont find it, continue to bottom ground level, locate the suit changer (if needed) and start as normal climbing your character up the building. 5. As you continue to each new "floor" be sure to follow the lego coin trails. Some will lead you to continued path, and other times it will lead you to around a corner where one of the doors are.
Since I began just collecting GOLD BRICKS, I haven't needed to look for those doors anymore since I find them while on my search for gold bricks.
It may seem obvious to some people, but is great in is simplicity if you cannot find a specific door - find every gold brick around that area, follow each lego coin trail, and you will hit it.
if by chance you already found a gold brick there earlier but missed the door, worst case youtube it..lol.