Is it necessary to change a DocumentRoot ? I would recommend to create an Alias for each project they have. Creating an alias is easy from Enduser Panel.
http://localhost/ampps/index.php?act=alias
Currently we dont have any provision to change the DocumentRoot. Though you can create a VirtualHost which will have its own DocumentRoot. Domains can be created from Enduser Panel too.
http://localhost/ampps/index.php?act=ampps_domainadd (don't forget to check in advance settings to add the entry in hosts file.)