My daughters are 6 and 7 but are complete opposites. One is quite and reserved. One is all diva. So one chose to put on a Barbie costume and the other chose an old granny costume.
For the Barbie costume we started with a large box and just cut it like a doll box, spray painted it and used wrapping paper glued to the inside for the background. For the granny costume, we bought a wig, got an outfit from Goodwill, and put on some makeup.