Personally, I would steer clear of any A frame design. I think the triangle area at the top makes for cramped quarters and makes it trickier than usual to place the vents where they won't leak water and/or allow for drafts in winter.
I'm very familiar with the Garden Coop site and I really like the design of their stationary coop. However, their tractor is way too small in my opinion for 3 chickens. I still think you need to allow for at least 4 square feet per bird indoors (coop), plus 10 square feet per bird outdoors (run), and if you live somewhere that winters will make it likely that your chickens will spend more time indoors, you probably need to try to make the coop area even bigger, or design the run so that it stays clear of snow and is protected from wind. I use 6 mil plastic, stapled to the side of the run outside the wire, where we live....but we don't get much in the way of winter here.
The problem, of course, is that a solid sided coop of this size, plus run, gets kinda heavy to be moved around the yard. And of course, you won't be able to move the coop around your yard at all during the winter months because of the snow, right?
What I would do is build a Garden Coop, stationary model. I think it's easy to panelize the construction so that if you need to move, you can unscrew the panels and take the coop down to bring it along with you. Then I'd build a small, lightweight day tractor to give the chickens the benefit of fresh grass during the months of the year that there is grass for them to graze on.
This is the arrangement I have (stationary coop/run with day tractor) and it works beautifully.