I think the only way to do it is move the ladder onto a new sheet called something like SYMBOLS LADDER, and move it in the sheet stack so that it is behind the top and the front to right wall, then use the same effect on that wall where you want the ladder to be visible. Color Key will work on the polygon that is the wall.

Then you might have to put some kind of a background WALLS sheet in there underneath the whole lot to add a back wall behind the bit you cut out.

Enixine, if you are ending up with that situation it may be that you are clicking in the wrong place just after you hit T.

Hit T, then click somewhere in the middle of where you want to trace, then back up to start the trace where you wanted to start it and click your second click to start tracing.

Until you cross the point where you first clicked the section the trace will appear to be going in the wrong direction, but as soon as you cross over that point it will flip to the right direction.

EDIT: ninjad by Remy :)

Once a polygon is shaded you can rotate it intact. the shading will stay aligned to that side of the polygon. Try it and see.

Looking good :)

Do you know that you can align the floorboard fills in those rooms that aren't perfectly aligned with the usual compass directions using Shaded Polygon (Angle by Edge) from the right click menu on the Polygon drawing tool on the right? (providing that floor isn't all one polygon). You get the tool and click the long side of the floor with it and the fill is instantly aligned to that edge.

The tool was originally intended as a roof shading tool, so each one of the floors now has a pitch like a roof. That is why they will have gone darker or lighter than they should be. Then when they are all aligned you type EDITSHADING, and pick them one by one and check the little box where it says "Shade only copy" and they will lie flat again.

Wouldn't it be interesting to have a 'click counter' app for the mouse so we could see how many were actually involved in making a map.