Marianne, I make mine similar to Rosemary. When I make the jumbled ones, I usually make them 9 1/2" x 9 1/2" only because that's how big my square ruler is! You want it to be small enough to fit easily in an envelope flatly.
Here is my wall with muggies.
And here is a jumbled one I made my sweet daughter in love. She loves Paris.
Have fun! If you'd like to trade, I'd be happy to trade with you.
geneva