Here's a demonstration of the standard roll stroke:
Here's another demonstration of how to play the roll stroke:
But Cliff Edwards played it differently, he started with the index finger followed by the other fingers with the pinky last. In his only instruction booklet 'Ukulele Ike's Complete Ukulele Method' published in 1927 he describes his technique.
Edwards explains in his book how he played the stroke:
"If you were to make a series of six consecutive strokes, in strict cadence, all down, in this order: index finger, second finger, third finger, fourth finger followed by the thumb then return up by the thumb, you will have laid the foundation for the very flashy roll stroke which very few amateurs know how to use."
He shows finger numbering here:
Watch him play his roll stroke here:
A very effective strum you'll agree! It seems easy to do until you try it. But practise makes perfect!