Hi Rattus, and a big welcome to the Forum. You'll find quite a few ideas on building runs and coops in some of the 'sticky' threads at the top of the General Chickens section, and there are lots of people on here who will be happy to advise and help. Also, do check out the excellent Poultrykeeper website, (link at the bottom of each Forum page) for interesting chicken info and help.
The space available in your garden will determine how many you should plan to get. For four hens you will need a run area of at least 6 sq. metres, 8 is better, 2sq metres per hen. Hens need as much space as you can give them, or else they tend to fight and peck each other's feathers out. Many companies sell little coops and attached runs which are impossibly small for the birds' needs and get knee-deep in poo in a very short time. Nobody ever complains that their run is too big for their birds!
Why not start another thread in the General Chickens section, then we shall all be interested in following your progress and ideas. As you may gather from the General Chatter section, we have a whole lot of new members ATM, because Practical Poultry Forum is closing down and people have moved over to here, so you're in good company.
The best way to see recent posts is to click on the Unread Posts button at the top of the Index page, saves trawling all through all the sections.