Chicken Coop Internal Space

Hi all. I'm looking at making another coop and run for three Lincolnshire Buff (heavy breeds). I'm planning to make to coop 60cm x 60cm, half of the space will be going to two integral nest boxes and for perches I will be using Hillfooters recommendations. Do you think this will be enough space? By my workings out there will be about 6 perches all at 30cm in length which is theoretically enough space for the three birds. The birds will have access to a run 2m x 4m which they will be out in all day. What do you think?

To be fair that was my concern. I'll make it a bit bigger and that way I can make more perching space. Thanks for that.