Ever tried putting a 3D-view of your building onto a sheet and ending up with something like this?
The vertical lines converge somewhere off screen and the whole thing looks very strange.

This has to do with the focal width of the lens. The closer you get to an object, the more distorted the image becomes.

When you move away from the object, the vertical lines become (almost) vertical again. Only... it's a bit small, isn't it?
This is where the focal length of the camera comes into play. Click F8 to open the wheel, click on the littel arrow on the bottom right and select Increase/Decrease Focal Length.
You'll get the ability to "zoom in" without adding the distortion effect:
Now you can make the view as big as you neet on your sheet and still have it look nice.

This method does not allow you to accurately set the focal length of the camera. But then, this is a visual thing anyway and you're much more likely to "play around" until you like the result than enter a fixed length into some parameter field or other. At least, I am.