Making a Paper Building: Step 2

Once I cut out the building, I prefolded the building. With the paper outside facing up, I used a ruler to anchor one of the sides along a fold line. Then I folded the free side up and moved to the next fold line.

 

Once one side it was done, I removed the ruler, flipped the paper over and folded the other way (i.e. the right way). You see the result.

Done