A post on the League of Legends Philippines website today announced a scheduled server maintenance on Wednesday, May 22 to implement Patch 3.7. The servers will be down from 3:30AM to 11:00AM according to the post.
Patch 3.7 will introduce a new Custom Item Builds feature as well as a few character rebalances. A Patch Preview video was released by Riot Games a few days ago detailing the new feature as well as a few of the character rebalances the patch will implement. You can watch that video here.
Full patch notes can also be found on the League of Legends Philippines website here.