There primary difficulty with scaling up a paper model is that the larger parts no longer fit on the same size pages. There are two ways to get around this:
The first is to simply use larger paper. So if you can get access to a large-format printer or a copy shop with one, print your scaled up model (say 150%) on a piece of paper large enough to hold it all (an 8.5" x 11" letter page at 150% needs a page 12.8" x 16.5", so depending on the margin, it *might* fit on a tabloid 11" x 17" page). See how you can quickly get to a point where you're needing *very large* paper?
The second method is to re-arrange the parts so they fit on the same size pages. Sometimes large single parts won't fit, so they need to be cut up and glued back together after printing. Here's an example I did recently - Mchale requested a USS Enterprise D model in 1:1400 scale. I upscaled Gary Pilsworth's model (originally about 1:2000) onto letter pages. If you want to see the new arrangments, compare the following:
PaperModelers.com - Downloads - USS ENTERPRISE
PaperModelers.com - Downloads - USS Enterprise NCC-1701-D 1:1450 scale
The basic premise is this:
You take a page of the original file and increase the size so now if it printed it wouldn't fit on a single page. Then you create a new blank file the same size as the original (make sure the resolution is the same as the original), and you start cutting and pasting parts from the enlarged page to the new original size page. They'll be bigger so you have to re-arrange things to fit. If a single part doesn't fit on the new page, then you need to come up with a way to cut it into pieces so it will fit, thinking about how you'll put it back together. I had to do that a couple times on the Enterprise example.
Does this help?