Its the hip that makes it look all a bit odd i think but i can totally see why it is irritating to spend money making it into a gable when in fact it gives you no usable room just a better looking house externally. The pitch to the top plan does seem very shallow which is going to compromise your rooflights to some degree. Of the two i think i would go with the pitch & flat combo as it will be marginally better looking and will give you a nicer vaulted space within the building. Have you thought about building a very modern extension? Still think that may be the way to do it, black framed windows / doors, high walls in grey render with totally flat roof - maybe put sedum on it to make it green and then get a massive roof lantern in the middle which will really brighten the inside up - wood burning stove and you got your self some Scandi-design. To take away from the height a bit get your builder to knock you up some brise soleil over the windows doors and bring planting as close to it as you can so it merges into the garden. Australians do modern on bungalows very well so i would look to them for inspiration.

Hi On first glance of your sketch plans, I would suggest squaring off the angle to form a simple rectangular internal light well. The angle can be a bit dated design style wise and leaves internal spaces a bit more awkward to finish. There are no angles in the existing flat so adding one in doesn't seem necessary. In terms of planning, I live in Islington myself and they are quite tight on issues such as building up to the boundary - like you have shown to the rear. You need to check if you are in a conservation area first off to assess if permitted development rights apply etc. We have recently obtained planing on our own house which was extremely contentious but on the upside, has meant we have got to know several of the planners very well! I could not comment on cost but know the resell value in N1 is circa 1100/sqft. We would be happy to assist on this in terms of making a pre-app or full planning application. If you are interested in obtaining a fee, please let me know by email. Thanks and I look forward to hearing from you Emma

Hi Tani, Yes, you can do secret gutters with a GRP flat roof system. I have designed one for a project about to start on site later this month. Some screen prints of my details below. Basically, I'm proposing to extend the flat roof joist out so it oversails the wall by about 300mm and have the ends of each joist chopped out to create a recess at the end. This recess is lined out with plywood and timber blocking and the GRP roof membrane is then dressed down and sealed up etc. Your architect / technologist / designer should be able to show this on their large scale section drawing as shown below. We are going to tweak the detail a bit so the vertical sides of the gutter are sloped and not at tight angles but apart from that what is shown below is how it should be built I think. You need to make sure the secret gutter is large enough for the volume of water it will drain away. You will also need a special hopper detail for the rainwater pipe to connect into and this will probably create a step out. I also suggest you use a good quality GRP roof manufacturer and approved installers, such as Polyroof. They have good technical support and worth speaking to them for advice also. It's worth spending a bit of time on this now to get it right and priced up properly before any work starts on site. Hope you get something sorted. I'll be posting some as built photos on here in the near future.

Concerns about tree roots could be from the neighbours or due to a TPO. We’ve been through this recently and have designed our extension to avoid the entire tree protection area (based on an arboricultural report-a requirement for us even to apply for planning). Despite that we have planning conditions on storage of building supplies (not near any trees), not being able to change ground levels (eg around patio areas) and being required to dig manually, not use diggers for fear of damage to roots. An arboricultural consultant should be able to advise on where and how you can build in relation to the tree, and then you would need the Council to accept the consultant's opinion. I assume the vendors must have had an opinion to plot the protection area? Also my understanding is that TPO legislation overrides permitted development legislation. As we've several TPOs, we’ve got to know the local council tree officers, but it’s the best approach as there can be heavy fines if you get it wrong.