What type of 'help' do you need ? Do you have something written that does not work or just want something someone else has done (a quick search on the Internet will bring many hits such as this one )
df -k | grep -v File | while read FS SZ US AV PER MNT
do
PER1=`echo $PER | awk -F"%" '{print $1}'`
if [ $PER1 -gt 89 ]; then
mail_user "Filesystem $FS is $PER1 percent full"
done