Servers will come down at 3 AM PDT for NA, 5 GMT for EUW, and 3:00 UTC for EUNE in preparation for the patch. Here is the Riot NOC announcement:
"On 09/04/13, starting at 01:30 PDT, ranked queues will be disabled in preparation for patch 3.11. At 03:00 PDT, the servers will be shut down and all games currently in progress will end in a draw and stats will not be recorded. We estimate the battlegrounds will be unavailable for 6 hours."Continue reading for more information on the changes, including map specific balance changes, undo in the Shop, new UI features, and MORE!
Here's Riot Pwyff with the full patch notes: