Castle puzzle

A not so simple puzzle about building a castle.

Controls

Left Mouse click.

1, 2 and 3 for fast selection of buildings.

R or Ctrl+Z to undo.

Tips

Dont worry too much about destroying buildings, they are easy to rebuild.

There are several hints, but they are not obvious.

The patterns for the buildings are either a cross or a line (3 width and/or height ).