Building a coop and have questions

[Luna bean]

If you could build one from scratch what size would you do? Im looking to have 20 birds max. Would a 12x16 coop be big enough for the birds and a seperate area for food bins to store food? We will also have a run attached off the side of the shed 16' x 8'

 

[DobieLover]

If you could build one from scratch what size would you do? Im looking to have 20 birds max. Would a 12x16 coop be big enough for the birds and a seperate area for food bins to store food? We will also have a run attached off the side of the shed 16' x 8'

I'd make the run bigger than that.
I house 23 birds in a building that is 8x16, 8x12 for the chickens, 1x4 for a built-in broody/maternity ward and some storage. The solid roofed run is 28x12 with two 4x8 annexes behind the coop, all open to the flock. My 23 birds do well in this.

 

[rosemarythyme]

A coop that size would be great for 20 birds + storage, but the run is too small. Your run is 128 sq ft, and for 20 you'd want 200 sq ft at a minimum (and more is definitely recommended, especially if you're going to be growing the flock over time).