The platform is 3600' it's a 3.54 degree slope and the descent starts at 9.7 dme.
I am not sure what do you mean by platform.
But "3.54 degree slope and the descent starts at 9.7 dme" is enough :
Ht diff = Slope deg x NM x 106.05 (here you get 3642 feet !)
if it is an ILS GS then
Ht diff = ( GS deg + NM / 120 ) x NM x 106.05
If you need a rate of descent then:
Rod ( '/min)= 1.767 x GrdSpd x Slope deg
and any time during descent a quick 3.14 deg slope NM = ( Alt - Elev ) x 3 /1000