I would strongly advise against trying to light a fire in a modern office building, I doubt that you could get rid of the smoke without letting in more cold than the heat produced by the fire.

Most modern offices are quite well insulated, and inner rooms are unlikely to get below freezing even in severe weather.

Before anyone gets too cold or weak, a search of the premises should be undertaken, with the following aims

1) to locate anyone not aware of the presence of others.
2) to locate any functioning UPS units, and turn them off to conserve the batteries
3) to locate bottled water and food
4) to locate spare clothing and blankets.

In all but the simplest premises, make a list of supplies that can be retrieved later.
Remember that the emergency may turn out to be life threatening, or relatively minor.
If only trapped for a few hours, dont rush to break into vending machines (theft, criminal damage, dissmisal) But DO locate the machines, and tools to force them, ready for later use if justified.
Dont cause needless damage to the building or contents in the early stages of a blizzard.
You will look very foolish if the power is restored and/or evacuation arranged promptly.

If the building has a restaurant or canteen, then forcing entrance would probably be justified, and there should be food supplies and perhaps a gas stove.

Sanitaion should not be much of a problem, since offices have large numbers of toilets. Use each one several times, and then flush normaly when utilities are restored.
If all else fails, then use waste bins etc as toilets, placing the used ones in a cold, unused area.

If bottled water is not available, then the water from toilet flushing tanks can be consumed in an emergency.

If anyone has a gasoline/coleman fueled lantern or stove in the car, perhaps for camping, then this would be very useful indeed.
The limited fuel supply can be supplemented with that found in vehicles.

Like wise if anyone has a kerosene lamp or camping stove, then this should be used, if fuel is short, then use diesel fuel from vehicles instead.
NEVER USE GASOLINE/PETROL IN AN APPLIANCE DESIGNED FOR KERSOSINE/PARRAFIN.
If useing candles or lanterns and camp stoves, have additional fire extinguishers to hand.
These should be found throughout any office, gather up a few extras.

Many large buildings have a standby diesel generator, if there is one and it is running, attempt to locate it and see how much fuel remains, It may be possible to obtain more, perhaps from trucks in the parking lot.
If someone in the party has suitable electrical knowledge, it may be possible to reduce the load on the generator by turning off lighting in some areas, this MIGHT allow the use of a small electric heater, coffee pot, or microwave oven.

If the diesel generator failed to start, it would be worth inspecting it and attempting to start it, especialy if the party includes anyone familiar with such equipment.

UPS units are often found in offices, and can be used to power any low powered line powered appliances such as laptops, desk lamps, cellphone chargers.
The run time is very limited.
It may be possible to use one or more vehicle batteries instead of the internal batteries, but TAKE GREAT CARE miskates can kill ! No point in surviving the blizzard but dieing of electric shock or from a battery explosion.

AA cells are often used in wall clocks, and it should be possible to locate a number in a large office.
D cells are often used in air fresheners in office toilets, and again a fair number should be available.

Whilst in an emergency it is probably acceptable to go through other peoples belongings, be resonable and dont read private papers etc.
Leave a note explaining what has been taken and why.