This article will go into how to add designers to LiveTiles design, including what permissions you will need to give them.
The Manage Groups Window
In order for a user to be able to create and edit LiveTiles Design pages the user will need to both be an owner of either the LiveTiles Owners or LiveTiles Design group.
1) Go to the LiveTiles Design subsite. The user will be taken to the LiveTiles Design landing page.
2) Open the Manage Tab.
3) Click on the Manage Groups tab.
4) Add the user to either the group by typing in the user's name and clicking the plus button