Insulating a garage

Hi I am converting my detached single skinned garage into a liveable area. Been watching a lot of u-tube vids but they don't make to much sense.here is where I think I am at.
FLOOR,
I need to put a 2brick course around the inside first, lay a plastic barrier 6mm down over,going up and over the 2 bricks. Think the insulation should be 100mm? Build a studded floor insulating between. Then board over. Need to then build a stud wall.
WALLS,
This is where I am more confused haha. Do I need to build a stud wall with a breathable membrane on the back then insulate with 50mm ?? Insulation then put a 6mm vapour barrier over that taping the joints to the floor.then plasterboard with foil backed board.
CEILING,
Unsure of the thickness here, but know I need to fit baffles and a couple of roof vents. Then vapour barrier again then foil backed board again.

Hope I am close with that but would love some advice.