This is an example of the directory layout for the chroot/uml directory of a SELinux UML instance.
This is the home of the uml user, it contains the script which starts the instance and the filesystems.
The swapfile and root_fs filesystem can be created using standard tools (dd, mkfs, mkswap) or you can downloads ready made root_fs images here. 

-rw-r--r--   1 uml-1 nogroup    root_fs
-r-xr-xr-x   1 root  root       start.sh
-rw-r--r--   1 uml-1 nogroup    swap_file