This is a simple oneliner to determine which user has used most diskspace in their /home directory
du -sm $(find /home -type d -maxdepth 1 -xdev) | sort -g
The result could look something like this
... 215 /home/userT 1367 /home/userB 10865 /home/userL 25326 /home/userY 116328 /home/userH 154426 /home/
The numbers to the left is size i MB.