I got some open fuse spots available...I am installing my bumper and roof lights.....

Bumper 110watt combined halogen bulbs
RoofRack Lights 220 watt combined halogen bulbs

what fuses should be used

Current = Watts/Voltage

So - 110/12 = 9.16A and 220/12 = 18.33A - I'd go with a 15A fuse for the bumper and 25A for the roof rack.

I will be grounding the lights to the body thats easy....but here is my next question

besides running 2 sets of power wire (bumper lights)
4 sets (roofrack LIghts)

can I not just use one???
will one single 16 gauge wire carry the right amount of power I need to those lights thus reducing the amount of wire I have to run/use....any problem that COULD occur

Here's the thing - where I am, we don't use the AWG wire sizing, so I'm not that familiar with it - I found a chart that shows ampacity, and 16ga is rated at 22A, so I'd say you're safe - just parallel the wires and crimp them.

Now, the bumper will typically bolt directly to the chassis, so grounding would not be a problem there, but I'm not certain how your roof rack attaches to the vehicle - so you might want to run a ground wire between the rack and the chassis.

Here's a nice chart on ampacity and wire sizes, and this one is for use at 12V.

The thing about low voltage wiring is that the currents are relatively high and voltage drop can become a problem as the length of the wire increases - this chart suggests that 16ga may be adequate for the bumper lights, but that you'd probably want something larger (or run multiple wires) for the roof rack.

As mentioned above 16ga will handle the current safely, but as the length of the run increases, the voltage drop will also increase and the lights will not be as bright as they could.