Here is how you should correct your model:
In the Stlye box, go to the edit tab and at the bottom is a drop box with Color next to it. Change the value to "by Axis" to turn the axis colours on.
Then delete all the lines that are black (these lines aren't straight) and replace them. This is easy as SU snaps to the axis easily (Blue - Z (Verticle) Red - X and Green - Y). Once you have one of these directions the line will colour to that axis colour (holding shift will lock the line on that axis)
Place the end of the line where you want it on the building.
Sorry if its a bit garbled not the best at putting it to paper.
Hope it helps.
ps Here is an image of what the model should look like.
1231corrected.jpg