bedroom over garage extension

[bp57]

we would like to build an extension on top of our existing attached garage. To have a 3rd bedroom and family bathroom. 90's built house, garage built at same time as house. Currently we have a semi detached house two bedrooms and bathroom central between two bedrooms. Bathroom small with no window. We would hope to turn the existing bathroom into a corridor to new extension, (as it really is that small!) and is to the side of the garage.

it is classed as a single garage but was built on an angle to the house so is almost double at the rear end of it. our garage is attached to our house and also to 1/2 neighbours garage as they are 'staggered'. As ours is a rather large angular shape it is also into the neighbours garden,on the plans our garage kind of 'juts' out into there back garden, with boundary fence running to just over half way along the rear of garage.Iit has a single garage door to the front and window and door to the rear into our back garden.

to make things slightly more complicated, the neighbours house is currently 'sale agreed' so we will be getting new neighbours!

we have never built an extension before but have renovated, so hope to keep costs down to get major building work done by prefessionals and do the rest ourselves as we have successfully before.

are we likely to come up against many issues regarding the extension technically being partly into there garden as our exsisting garage is? i keep reading about boundary lines and certain metres away but how does it work when the garage is attached to neighbouring property?

Please excuse my lack of knowledge, i am new to extension, my partner knows more but he is computer 'unfriendly!' so im trying to research as much as possible with lack of knowledge! :oops:

thanks for any help.