I'm getting 30 bantams come October-ish how much space do I need to expand my coop?

[Lost praetorian]

The regular chicken run is a 8x9 not including the coop which is 9x5 (in feets).
But I'ma build a separate one for mah bantams. I'm thinking a 9x15 run for them and a standard 9x5 coop. That's good innit?

For reference, I ordered 10 blue frizzle Cochins, 10 blue silkies, 5 assorted Japanese, and 5 assorted frizzle Cochins bantams.

 

[Lost praetorian]

Oh, and I plan to let them roam the yard on days when it's not raining just like I do the big chickens.

 

[NatJ]

I would recommend a minimum of 2 square feet of floor space per bantam in the coop.
9x5 makes 45 square feet, so that's only big enough for 22 bantams (unless feeder, waterer, and nestboxes are taking up floor space-- then it would hold even less bantams).

Your bantams will probably be about half cockerels. If you remove most or all of the cockerels, you might be fine with the amount of space you have planned. You can sell the cockerels, give them away, butcher them, etc. But you'll want to do it before they all start trying to mate with the females.

If you want enough space for all 30 bantams, plan on at least 60 square feet of coop space (6x10 or 7x9 or 8x8 would work.)

For the run, I would recommend 5-10 square feet per bantam.
9x15 makes 135 square feet, so between 13 and 26 bantams can use that size run.
Bigger is always better, so I would suggest increasing the run size if you can.