If you are in the UK, try https://www.houzz.co.uk/ Some construction is geographically specific.

@apple_pie_order we are based in south west of UK , Did you mean some councils dont allow garage conversion ?

Many many locations do not allow garage conversions as garages are not built to the same habitable space standards as are homes. Bringing up a secondary storage unit to the stability, comfort, and all standards for a residence often results in tearing down the accessory structure in order to rebuild it with the foundation and framing that can bear live weight and support the electrical, plumbing, and other required elements.

If the garage is allowed to be converted to living space, it's often done very expensively, poorly, with it being obvious, and kinda ugly, because there's no other place to park the cars other than the big ugly drive that stops directly at the garage front. Garage conversions only really are attractive when another garage is built, with a new driveway to them.

Absolutely check what’s allowed locally. People convert garages often where I live so this isn’t a wild request to me at all. Many people can’t see past their own experience to realize what can be done.

You start by finding out what you can do where you live.Garages are rarely approved for actual living space other than maybe a man cave. There are codes to be met . Not inpossible but be prepaerd to have to dempolish the garage and then do what you want if allowed . It would then become more of a ADU . BTW in the UK it gets even more complicated with all kinds of issues regarding permits. NO matter where you live the garage has to meet code for sure and that can be a big issue even where West Coast lives

Of course it needs to meet code and I said to check locally what is allowed. But the doom and gloom on this site about garage conversions is often regional and people need to realize that. Just like the basement debates where those without them can’t imagine them and have narrow views on them as a result.

A larger floorplan could help. It appears the garage is a separate unconnected structure with a long section not for car parking. Besides the plans can you post exterior pictures of the different sides including the house.

You also need to know about lot line setbacks. In our area all buildings must be 10' from the lot line, As a garage it may meet the set back regulations, as living quarters they may not. Also the garage may have been in place when the restriction went into place. But as new construction or remodeled, it may may need to meet current regulations

If the picture is your house and garage, they don't match the floorplan. This'll be tough.