I'm sorry your dilemma got missed! Are you butting your loft extension up to next door's or are you having a gap? I wouldn't chose slate as it will clash with your roof tiles. You could have the same as next door, but with your style of window in it. Or you could have brick edges so that it ties in with your exposed brick lintels above your windows, with the rest render. On the bottom, you could have brick or block and render ( the second one's cheaper ), as either will fit with your house. The brick finish would stand out, the render would blend in, depends on what you fancy.

You've got some tricky dimensions to work with there. So before you go ahead with a design, you may wish to contact one of the Concept planner's on here, who will help you see where to put things, work out the walk room needed around objects and help iron out the flaws before you build. Karen at OnePlan comes highly recommended on here. There are a few points to look out for as I see it. The width that you have left over from Bathroom wall to outside wall of 2887 isn't that long. A bog standard king size bed is usually just over 200cm with the covers and may be more. That wall also, isn't particularly wide, therefore, if you wanted bedside tables, it could be tricky to use that space. So, putting the bed on the back wall, which will probably look nicest has other problems. Easier to show in diagrams ( hopefully ). I can't see how big the nib is at the top where i've put a couple of Chests of Drawers . I know we couldn't manage without them. I feel the large window is too big, and if you're going to put wardrobes on that wall, then you need to make sure the window isn't to large and that you leave a big enough gap either side for not just the wardrobes, but also for any window coverings. You don't want to be pushing curtains in to wardrobe doors and not having enough room for poles. I'd make the bathroom a little smaller to get better walk room in the bedroom. Unfortunately, Architects rarely think about furniture placement, I personally think it's paramount in considering the sizes of walls, windows and how to live in a space. However, i've done many a build in my time, so I know the pitfalls. Concept planners will help you with all of these problems.

@Roomhe3-by-Room (UK) Ltd thank you for your comment. I did a rough mock up of your suggestions on PPT and the slate tiles and dormer with grey windows makes a dramatic difference. I really like the look of it! The current concrete roof tiles we have are believed to be original from the 1950s when the bungalow was built, and if I have done my research correctly, it has to come to an end of its life span of 50 years so it may be worthwhile to redo the roof too. Would love to opt for slate tiles but have heard these are more expensive than concrete tiles. We don't have a big budget but would like to go for something similar in appearance and durability as slates at a lower cost. Is there something on the market that fits this profile like concrete roof tile in grey slate colour? This is my first building project and knowledge of materials is very limited! Thank you

Have any of the other houses on the road, or neighbouring roads, done anything similar? Could the dormers be towards the back so that they “create the space” but the window could be in the end gable wall looking out the back?