The lords of the Philistines gathered them together to offer a great sacrifice to Dagon their god, and to rejoice; for they said, Our god has delivered Samson our enemy into our hand.
"Now the house was full of men and women"  (Judges 16:27).  The purpose of this verse is to stress the size of the crowd.  It was a "capacity" audience and then some.  The three thousand people on the roof seems to have been a very unusual accommodation for such a number of people, and it no doubt contributed very substantially to the number of fatalities following the collapse of the temple.