I have worked on several projects lately that were blown up. That is to say I worked in 1 inch to 1 foot scale. When I'm working on something that will be "blown up" or enlarged 1200%, there are some different things to consider. First on the list is distance. If something is going to be 35 feet long, chances are it's going to need to be seen from a distance.
Thinking back on the many billboards and station dominations I've done also helps. I find myself often referring to lessons learned when solving problems with type, design and distance.