^^^ I've got a wagon too, and I know first hand what GRNMTNRS is referring to in pont#3 If you have installed, or ever plan on installing springs that lower the ride height, your tires will rub the lip of your fenders. Having them rolled means to actually round the outwards to give more clearence. 215/18/40 is a significant jump in diameter from the stockers and going up to 225s has even less clearence on the outer tire edge. If you drop the ride height, the distance between the fender lip and the tire is reduced.
Keep in mind, the wheels offset has a crucial part in the equation also. the stock wheels have a 55 offset. If you decrease the offset, the wheel moves in towards the car and will tuck it under the fender better. You need to be very careful because going too little on the offset will cause the tires to rub on the inside of the wheel wells. I still have the stockers and I need to roll the fenders. I've read the offset for the 18s should be no less than 45, and 48 is optimal.