I have 6ft by 9ft kennel style runs (ie roofed) with raised hutches of 3ft deep by 6ft wide in each . .so they can use all of the bottom area, plus the hutch plus top of hutch (as all are ramped).
I have 4 buns in each of these and they are very happy with them.
Used to have larger aviary style but tbh they only used the sheltered parts of those so we swapped.
They also get a couple of hours lawn time most days - though less some days.