For a double decker carousel, just drag a second carousel ontop of the first one, or you can hold shift to raise or lower it (this also works well for scenary). For an entrance, I usually go to scenario editor, and zoom all the way out, then I click on owned land, then hit the + sign until it is a maximum (the buying land + sign). Then buy all of the land possible. I think it will say 150 x 150, thats all you need. Then select all of the rides, and scenary. Then go to the entrances choices and pick out the six flags entrance (it has 6 flags on top of it). I have attempted SFGAm in RCT2 many times, and the best one was when I started off with a bunch of short LIM launched rides, to get alot of money. Then I built a bunch of the rides, and knocked down the ones that aren't really at six flags. After finalizing the park, it was on year 16, so it will take alot of time.