Another option is to look for a free or cheap building, maybe on Craigslist. For 6 chickens, you are looking at something in the range of 24 square feet minimum. A little bigger would not be bad, but you have to be able to transport it. I'm not sure what your climate is, but for most of us, a wood or metal building would work. If you are in a colder area, maybe wood would be better. Once you get the building itself, finishing it off is not that hard. With six hens, four feet of roosts, two nesting boxes, and you are on your way.
If you are building from scratch, I suggest trying to stay with 4 foot or 8 foot dimensions. Most building material comes in 4' or 8' sections. Using these as your primary dimensions cuts down on waste, maybe cuts down on cutting, and you get a larger size for practically the same cost. Be careful. The 4' and 8' dimensions are out to out dimensions, not centerline dimensions. If you build your from with 4' or 8' centerline dimensions, it is a bit too big. Ask me how I learned that one.
Also consider how to do your roof. You really want an overhang so you can cut vents right at the top of your walls and have rain protection. If you build the rest say 4' x 8', the roof might get a bit more expensive. To me, it would be worth it, but something to consider. A sloped roof drains a lot better thana flat one too.
To me, for six hens, a 4' x 8' coop would be tremendous. However, if you build it 4 feet tall, you need to build it so you have access to all parts of the coop, partly for cleaning purposes and partly to be able to reach anything anywhere in there. Hinging one wall to either lay down or raise up is one way to achieve this. You could make a people door and go in, but that would be cramped.
Just a few thoughts. Good luck with it.