Can I safely leave male/female plugs exposed on a rooftop balcony?
Safe?  Well anything plugged in outside is going to a GFCI protected outlet right?  So that should provide some safety when everything is wet.  The open female ends might trip said GFCI if they get really wet, so it would be good to cover those up or just turn off the circuit when rain is expected.

The other issue is corrosion and... spiders.  Most of the metal that plugs are made from will corrode over time when they get wet.  You will start to get poor connections which can lead to sparking inside the plugs which leads to even worse connections, etc.  The other issue is tiny spiders and other bugs getting inside the plugs and making them dirty on top of the corrosion.

They make small water resistant cases for extension cord connections.  They pop up at home stores during the holidays (for outside light strings), but some places carry them year round.  Keeping a case on the female end will help.  Using some anti corrosion spray and cleaning the contacts regularly will also help.