Well in my view before inflating the bag you should check if anything is above you. There is little point putting a bag up if you are under a piece of wreckage. Safest and easiest time to do that is before you are working against the buoyancy of a semi-inflated bag (particularly in the case of the 4.5 ft ones we use for all ocean diving in the UK).
The bag is then inflated and ready to go - at that point the team can help you by checking above (which is briefed to them before the demo). They are best placed to look up for you and make sure the overhead is clear. Like everything team diving applies
Hope that helps.
Cheers
Al