There's a neat little 1st level Dru/Ran/Sor/Wiz spell called Blockade in The Complete Scoundrel
that as a Swift Action conjures up a 5' x 5' x 5' block of wood (with accompanying stats, and caveats to stop you dropping it on people) for three rounds.
Given that it seems amusing but there are no metamagic feats other than Extend, Persistant, Twin and Repeat that can affect this spell, I'm trying to think of what a "Mass" version of this spell should be. Not swift because high level spells tend not to be. Using Mass Unseen Servant as a basis, a 4th level spell could do 1 block/level, but that seems weak given the wall spells that are available at 4th level: you would need caster level 16 to surround a 5' square to a height of 10', and the ability to build a staircase 25' high is a poor substitute for Fly. Maybe a 3rd level spell? Nerfed to 3 blocks + 1 per 2 levels? Requiring the blocks contiguous, and at least one of them in an adjacent square to the caster (Blockade itself has Range 0)? Bump up the duration to six rounds?
Opinions? One thing I want to avoid is a random element in the number of blocks that appear, however much fun it it would be to Empower, there's a limit to how long other players are prepared for you to rearrange dics on the battlemat and that time can be cut down my allowing you to know how many blocks you have to place before your turn.