[Borge Reroll]

I've been thinking about getting some chickens lately and been looking at a lot of coops and it gave me the idea to turn one of these storage boxes into a coop. Is that a terrible idea?
Was also wondering how many chickens it would be suitable for? We are thinking about getting 4-5 I think the breeds we want are easter eggers and/or Plymouth rocks. 

Thanks

[New shoot]

It is no doubt possible, but I wouldn’t consider it particularly great housing. 

They are not cheap, but I have plastic coops that are designed for the job - an Eglu and one by Green Frog. I had wooden coops before this, but would not go back now.  Here is a link for Green Frog as they are not half as well known as some suppliers and you might have missed them in your reading.

https://www.greenfrogdesigns.co.uk/chickens-ducks-geese/

You need enough airspace and ventilation for the hens, without allowing draughts or water in.  You also need nest boxes and perches for them to roost on. 

There is a review of the options on the main site you might find helpful.

https://www.chickens.allotment-garden.org/poultry-housing/

[upert]

It occurred to me after a recent infestation of red spider mite that a modified £40 storage box might be doable yet there are several things that could make it awful if not done right. Plus, it's a bit small. I've always had nice roomy wooden coops and I clean regularly, yet the price of things is pretty high even if I build a new one of my own out of wood if I can get it.

There is a breed of allotment people, of which I am one, that do their allotmenting as cheaply as they can. Some things are difficult to skimp on though, however enticing it might be.

[perris]

I second New Shoot's advice.  A Green Frog coop may be expensive, but they are very robust and hold their value (look for a used one online) so you'll get it back when you want to retire from chicken keeping. They are also very easy to clean, the importance of which you will only appreciate once you've started doing it 

[grinling]

I used Hillfooters slurry, look under search at top, never had remite again.
It also helps to keep wild birds away from the coop