Preheat oven to 375 Degrees F. Grease the back side of two large cookie sheets. (You will need to roll your dough directly onto your cookie sheet so you need to use the back side of it.)
In a large mixing bowl combine flour,ginger,allspice,baking soda and salt. Set aside. In another large mixing bowl cream butter, shortening and sugar. Add molasses and mix. Add eggs one at a time mixing between each addition. Mix well. Gradually add dry ingredients to wet and mix well. Remove dough from bowl and place on a sheet of plastic wrap. Wrap and seal well. Place in fridge for 2 hours to overnight. (I always make a bunch of batches one day and wrap and store in the fridge. Then I bake them at night throughout the week.)
Once you are ready to bake your gingerbread, break off a small amount and knead it with your hands to soften it. Then place it on the back of your prepared cookie sheet and use a rolling pin to flatten to about 1/4 inch thickness. (You may need to dust dough surface with flour to keep from sticking) Place pattern on the dough and cut around the edges with a sharp knife. (I usually can fit two pieces per cookie sheet. Just make sure you leave about a1/2 inch space between the pieces because the dough will expand when it bakes.) Carefully lift the dough around your cut out piece and remove it with a butter knife or small offset spatula. Place dough back with your remaining unused dough. Bake on center rack for 8-10 minutes. You want to make sure you bake it so that it's crisp. If you under bake your pieces your house may sag when you try to put it together.
Loosen your baked gingerbread pieces by carefully sliding a spatula under them, immediately after you remove them from the oven to prevent them from sticking to the pan. Once they have cooled for about 5 minutes and are not soft anymore remove them to a cooling rack to completely cool. (Make sure you use a very large spatula since the pieces are so large. This will help support your cookie.)
Continue until you have four of each pattern piece and you will have enough for 2 houses.
Make sure you wipe off your pan and add more grease between each batch.
I usually store my pieces in disposable aluminum baking pans, uncovered, until I'm ready to use them. Remember you don't want your pieces to soften. They need to be crisp and sturdy for building.