Cream shortening and sugar in a stand mixer. Add egg and molasses.
Add vinegar, baking soda, salt, and spices. Add flour gradually. (You may need to knead in the last cups of flour by hand.)
Pour 1/4 cup or so of vegetable oil on a large, heavy baking sheet with sides (a half-sheet pan -- about 18"x 13" by 1" high -- is perfect). Roll out dough with rolling pin until it fills the baking sheet on all sides and meets the corners. (A standard size rolling pin will fit perfectly across the width of the baking sheet.) You should keep adding vegetable oil to the top of the dough as necessary to help it roll out slick and smooth. Remove any excess dough that does not disappear beneath the rolling pin and mesh flatly into the pan. Use that dough in another pan of gingerbread.
Place your pattern pieces on top of the gingerbread and cut gingerbread house pieces in gingerbread using the tip of a knife (wipe the knife clean in between cuts, if necessary). Leave all dough in the pan. Cut your pieces to maximize the available space just like you would if you were using cookie cutters to cut sugar cookie dough. Pieces can share sides without space between. You don't need to separate the pieces from the surrounding scraps at this time, leave them in to keep the pieces from spreading and changing shape. Just be sure to cut all the way through to the pan as cleanly and precisely as possible.
Bake at 350 degrees F until very well done (remember, this is for building, not for eating, and you want it dry). Depending on your oven and other factors, this can take as little as 20 minutes or as much as 35 minutes or more.
When you pull the pans out of the oven, re-cut your shapes in the gingerbread (if you don't, you won't be able to separate your house pieces from the surrounding scraps when the gingerbread has dried).
Let gingerbread cool in the baking sheets until it's no longer too hot to handle. Carefully remove the house pieces and set on cooling racks to cool completely. Ensure the pieces do not touch each other as you want the air to be able to circulate freely to dry everything out. Now is the time to pop out the 'scraps,' before they become hard. 'Scraps' are the parts you don't want: the insides of windows, spaces between fence rails, etc. Remove the front door, if desired, but don't throw it away. You can include it later when you assemble your house -- a front door can be a fun part of your house to decorate!
Leave the gingerbread out to try. (Leaving it on cooling racks is ideal so that the air can circulate on all sides.) Gingerbread used for building should "season" about 2 weeks before being used to build with so it can dry out. Dry gingerbread is stronger and will support more weight. If you're pressed for time, or if you're building a small house, you can get away with letting it dry overnight, just be sure to limit exposure to moisture and humidity by carefully choosing where you leave the pieces to dry.