I have been charged with the task of designing a series of large scale 5' by 8' banners that will be hung on the exterior of a building staggered from the 2nd floor about 20' up to the roof about 60'up. They will be viewed at multiple levels, ground floor primarily, but can also be seen from the windows of each floor, and looked down at from the roof. The banners will only feature text.
Does anyone have any advice about special considerations to make for typography at such a large scale? I am primarily concerned about legibility. What would be an appropriate type size for something displayed up to 60' away? and is there any treatment done to acommadate the viewing angle? Are you aware of any literature on the subject?