Well you can never guarantee 100% safety simply because you can't account for stupidity... But to make it as safe as possible, before you even start you would want to select a contractor with a robust health and safety policy and a good safety track record in constructing similar structures. Then you would want a method statement and risk assessment to demonstrate how your particular building is to be constructed and to show that the contractor has identified all the risks. With regard to working at height, your workers will need to be properly trained for such work. Fall protection is a must - hard barriers should be placed around the edge. Workers near the edge should be tied off 100% of the time, preferably with self-retracting lifelines, and should be supervised at all times. Falling objects can be avoided by placing toe-boards and/or netting around the edge. Loose materials should be kept in proper bags or containers. Tools should be fitted with lanyards and tied off to suitable anchorage points. Finally to protect passers-by you should preferably implement an exclusion zone. If that's not possible then install a crash deck to catch any falling objects before they hit the ground (or someone passing by).
That's a brief summary and I'm sure there are some things I've missed, nevertheless it should give you some ideas as to what is required.
Yes, in my experience scaffolding is the most common type of edge protection. You could fix the uprights to the steel beams/columns and run scaffold tubing as handrails and knee-rails, with scaffold boards as toe boards