You have to use one of the side views when supporting to make sure your beams are vertical, if that's what you mean. If you are using the 3d view, your camera will be at different angles so "vertical" will be slightly different that the next beam over. Also make sure you make all the beams vertical in one side view, then go to a view one quarter turn to the left or right of the one you were using to make sure they arent angled that way either.
Here's what I mean: