Welcome to BYC.
It's great that you're doing your research first and asking for recommendations instead of jumping in head first and buying one of those tiny, ill-ventilated, shoddily-build prefabs.
To give you better advice we'll need to know how many chickens you're planning on having, what level of building skills you have, and where, in general, you're located. Climate matters, especially when building a coop.
In general, each adult, standard-sized hen needs:
4 square feet in the coop,
10 square feet in the run,
1 linear foot of roost,
1/4 of a nest box,
and 1 square foot of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on their roost.
Some rules of thumb:
- If it looks like a dollhouse it's only suitable for toy chickens.
- If it's measured in inches instead of feet it's too small.
- If your walk-in closet is larger than the coop-run combo you're thinking of buying think carefully about whether you have an utterly awesome closet or are looking at a seriously undersized chicken coop.
- If it has more nestboxes than the number of chickens it can legitimately hold the designer knew nothing about chickens' actual needs and it probably has other design flaws too.
Good luck!
P.S. If you click the "My Coop" link in people's profiles you can see what our coops look like.
