Aggie Stadium An upper class or grad student in environmental design or such put together a thorough study and proposal a number of years ago on how to tweak and improve AS, including some options for shade.
As far as cementing in the end zone, I'm not sure we'd gain more than we would lose. Say a thousand people sit in the grass, and cement gets us 2,000 poor-sight seats... that's not a big bump.
A double deck over the student section could add 4-8,000 seats (realistically), would add shade for the lower level, and probably would add restrooms and additional concessions. Maybe even reception boxes and great sight lines.