double sides dormer loft conversion

[LLL]

I plan to buy a property but it is small, if I can do the dormer loft conversion on the first floor, it can add space and bedroom/bathrooms. However, I am not sure whether is is practical since it is very important for me to decide buying the house. The plan is on the right-hand side on the second floor, two smaller dormers can be added due to the stairs. On the left-hand side, a full-length bigger dormer can be added. The upside can be split into two smaller bedrooms, and on the bottom side a big bedroom with an ensuite bathroom can be built. I may even can add a bathroom in between (the landing area).

I would like to know how difficult to get permission from the council to do the project. The right-hand side is a meadow so there should be no objection, the left side faces a small window of the neighbour and I assume it is a bathroom or the stairs.  I saw there are some similar extensions done in this area but might be many years ago. 

Any one can suggest how much it might cost? and how long it will take to complete.

thank you