Many site owners has to share their Webmasters account with other colleagues. In such cases you may not want to share full access of the account with them. To help you, Google has now started providing this facility where a site owner can add users with limited workings.
Though you are not allowed to choose a custom set of privileges, but can opt one of the three available choices. These option has predefined set of rules for different level of accounts. The three types are: 1. Site owner, 2. Full user and 3. Restricted user.
To Add a Full/Limited Access User
Go to Users (in left sidebar) and click on ADD A NEW USER red button. Give an e-mail address and choose the restriction level.
To Add a Site Owner
On the Site's home page in Webmaster Tools, click Users and then go to Manage site owners link.
In the Verified owners section, click Add an owner. Type the e-mail address of the owner you want to add, and then click Continue.
Change Existing Users
Permission level of existing users can be changed very easily from the Users page. Just select the appropriate type from the box right after the user e-mail.