If you want a high quality well designed house try Forsham Cottage Arks at Ashford who are regarded as the market leaders in traditional coops. In particular see their Lenham 504 mid sized house which isn't cheap but I've had three of their houses now and can't fault them for durability (the oldest is over 10years old and still sound) ease of maintenance cleaning etc and well thought out husbandry. They aren't cheap though but if you look at the features they have it'll tell you what a well designed and built house should be.
http://www.forshamcottagearks.com/ .
Also I've seen and been very impressed wth the build quality of the Westaway poultry houses which are built to order and again look well thought out by people who know poultry,
http://www.westawaypoultry.com/products/housing.html again they aren't cheap but built to last.
I'd echo what jonesblack has said about cheap ebay imports from china which are very flimsy. For example they use 10mm tongue and groove rather than 12mm or better still 15mm. Steer clear of any which use mineral felt (roofing felt) as they will be a paradise for red mite and you'll rue the day. I'd also caution about carpenter tradesman type house built by someone who might know about wood work but not about chicken keeping. There's a lot of knowledge goes into a well designed house and it's not all about build quality and sound materials though that has to be right. I've seen lots of well built disasters and DIY efforts which have failed to appreciate the needs of the chx or been well made but used the wrong materials.
The interior features are very important such as perches which should not be single poles but a grill through which the dropping s will fall and a dropping area which should not be accessible to the chx. Many have dropping boards which sound convenient but are often flimsy and warp, awkward to handle particularly in a wind and if not deep enough can end up having their contents scraped off when you withdraw them. If they are too big they can be heavy and difficult to tip into a barrow without spilling the contents.
I think the best designs have a removable externjal nestboxes and a completely flat raised floor which is readily accessible and easy to sweep out with no ledges to trap droppings.
Pophole doors should be vertically dropping in slides which don't jam and can be fitted with an auto opener in the future. I wouldn't touch a house with a side sliding door personally.
I'd always prefer a double pitched roof too. Ship lap or corrugated mineral board (Onduline) is very good. I've seen some disasters in this area too with the roof slopes shedding rain over the entrance.
You also need to think about how you are going to manage the run. Will you need to move the house to a new site and how frequently. Small tent like arks can be fitted with wheels or houses such as Lenhams can be mounted on sledges as I do and towed to new locations. 8 L/F chx don't need a lot of room and an area largely comprising roosting bars of 9 square feet is ample. There's no need to make the house too big if you have ample run and they prefer to huddle up in winter or on cold nights so it's counter-productive to give them lots of space and in particular they don't need much floor space just enough to allow them access to the perches and nestboxes. Too much space and it will be cold and use a lot of litter and encourage them to scratch about in it when they'd be better off in the run. Make sure there's well baffled ample ventilation above head height and all will be well.
I agree with Karlooben. get a shed if you don't want to keep birds in it but otherwise get a good quality chicken house.
All the best
HF