Hi. I'm thinking of converting part of my garage into living space and
would like some advice. I'd like to do as much of the work as possible
myself, but I'll probably need to bring experts in for some parts (my
plastering and bricklaying is functional, but not pretty!). Here are
the facts.

Double width garage with two single doors. I want to convert one side.
Area is probably about 20ft x 12ft
Need to remove one garage door, brick up the hole and put a window in.
Create partition wall between two halves of garage, with a new door in
the partition wall giving access to the new smaller garage.
The fusebox is in the room, so wiring should be straightforward.
Need to bring radiator feeds into the room.
Need to board ceiling

What sort of cost am I looking at if did these jobs myself or asked a
builder to do them? E.g. is there a good rule of thumb pricing for
brickwork or partition walls?

What sort of pitfalls should I look out for?

Would I need planning permission for this?

Thanks in advance