The Buttercup farm one looks very similar to my main layers house but mine has a bigger window for ventilation and the nest boxes are lower. I've got this one:
http://www.chicken-houses.co.uk/view-product/The-Newton-Chicken-Housewith 11 (big) chickens in it at the moment which is a nice number. I wouldn't fit 20 Orpingtons in there. I think it would be too big for three but it's nice to have room for expansion and I like all of their designs- I've got a smaller house that I use for broodies too. I have had red mite problems with it though & have now taken the felt off both the main roof and nest box and replaced with onduline as well as creosoting it yearly.
I think every house has niggles but this one has fewer than many - and most of the issues come when you're trying to assemble it and nothing fits (ironically the cheap and cheerful Chinese ones are sooo easy to assemble).
My best houses are Wells poultry houses but I think they've gone out of business now. Really solid but with the onduline roofs already so better ventilation. I've also got a Jim Vyse ark for the ducks but not a big fan of arks so won't go there again - I find them a pain to clean because you have to crawl in through the hole. I think Smiths Sectionals tend to do bigger houses with runs attached - I've looked occasionally but never found quite what I wanted.
I also have three 8'x6' sheds which I use for geese, turkeys and ducks and they are great. Easy to access but they do take a lot of bedding which is fine if it's full of 12 geese but might not be so cost effective for three chooks!
Good luck deciding - I think if you go for a solid wood build (make sure it is treated wood) and ensure you have good access for cleaning and the birds have enough space, you'll not go far wrong. Nothing is perfect but you mainly want something that lasts.....
H