I'd personally go for the modern home with a partial view of the woods! Floor to ceiling windows and geometric architecture. Of course, in this dream world, the house would be located where it could receive daily unobstructed sunlight and the it would be build with green technology. :)

If you are working with white and grey already I think it would be good to introduce some colour warmth via the floor. An engineered timber floor would be warm underfoot but if you have underfloor heating them perhaps some natural clay tiles treated with boiled linseed oil. This looks beautiful and is warmer underfoot that normal glazed ceramic tiles but does require occasional maintenance, not unlike a timber floor.

Another recommendation for Karen @ OnePlan even more so if you're going back and forwards as she can show you a few ideas. Everything really seems set in stone bar the plant room? There also looks to be stairs on the gable end which I assume you need for letting the dogs out? My (very non-pro!) comments on your green plan. I'd reduce the plant room depth to 1500 and the gap between the island and units to 1200. I'd access the plant room from the larder end so lose the corner cupboard. I'd put the oven at the end of the sink run and just use shelves to balance the gap between the oven and window. It means losing the window seat however just thinking it would actually work better for extra seating in the living room? I'd go for a smaller hob and have it on the island away from the stools with a downdraft extractor. The living space is a little tight but assuming you're having a tv I'd hang it against the play room wall then chose a slim chaise sofa without arms so it doesn't visually close the space off coming up the stairs. I know sofa arms shouldn't normally overlap but I think it works with window seats. You may also be able to fit a small accent chair in the left corner next to the tv and then have a sideboard on the plant room wall for extra storage.

I think a flat roof with a terrace above would be amazing! Flat room materials have really moved on and such good quality now. Or you could do a flat roof with skylight or roof lanterns which will give lots of light. My sister has done this. Her extension is flat roofed and it looks really smart. Also I think if the extension is no higher than 2.5m it can come under permitted development? There are other criteria but your local council planning portal should have all the info you need. Pitched roofs would be more expensive. My garage cost £15,000 but with a pitched roof and tiles it would have been nearer £25,000 and I would have needed planning permission. Here’s some ideas for you