Greetings Cyclone733;
For us on the B747-400 the flight planning section in our OM-B states:
"Average APU fuel flow rate under normal operation on the ground is 300 kg/hr."
No specifics on the influence of load on fuel flow though.
For example 1 or 2 generators on line (not much difference on the freighter I guess as normally gen 1 is the only one on line. Gen 2 is then used for main deck cargo handling) or 1/2/3 airconditioning packs running... I reckon bleed demand has the biggest impact on fuel flow.
Other aircraft:
MD-11: 200 kg/hr on the ground
150 kg/hr at altitude
B767-300: 115 kg/hr
TS737