This is the coop or the link I should say
https://overezchickencoop.com/collections/chicken-coops-1/products/extra-large-chicken-coop
OK, that's 5x8 if those measurements don't include the nestbox or 4x8, if they do include the nestboxes. The latter is more likely because lumber comes in multiples of 4 and the company wouldn't be throwing out 3 feet of every standard 8-foot board to make a coop that's 5 feet wide in actual floor space so I strongly suspect that they're measuring the footprint on the site including the nestboxes.
4x8 is 32 square feet, enough for 8 chickens, not 20.
It is also the size of my Outdoor Brooder: https://www.backyardchickens.com/articles/using-deep-bedding-in-a-small-coop.76343/
Here's a photo of it with chickens in it so you can get some idea of how much space you'd really have:
BUT, the chickens in the photo are 8-week-old chicks, not adults, who will be at least twice that size. Still, I think you said you have 6 chickens, so that would be adequate space.

OverEZ coops have a reputation for being sturdier and better built than many purchased coops, but in addition to the size being WAY TOO SMALL for the number of birds they claim to hold, they are very poorly ventilated. The windows are cute, but the operable section is tiny and it's down low rather than up at the top where it's really needed (heat and ammonia both rise).
I don't remember if you said where you live (you can put your general location into your profile because climate matters). In my climate the 16 square feet of permanent, 24/7/365 ventilation in my brooder -- double the recommended minimum -- is inadequate unless I shade the coop. If you live in an area with harsh winters you absolutely need to have your ventilation up high so that there aren't drafts on the birds and so that the warm, moist air the chickens generate can rise and escape rather than having the moisture freeze on the chickens' combs to cause frostbite.
Good luck figuring out your best option.
