if you want to be able to open the doors, load the boot and walk around i think you need at least 9m x 7m but if you to also want useable work benches and storage spaces (eg for the lawn mower etc) add at least 1 m to width and length

I'm sure there's plenty of confusion about the why's and wherefore's of house orientation. The reality, as I have recently discovered, is that if want to live in an area that is older, developed, close to facilities, you take whatever orientation the block actually happens to be and do the best you can with it. Unless you're out in the country, or buying something in a new estate, you may not get a choice of orientation: we certainly didn't. And yes, our garage does have the best aspect - because there was nowhere else to put it - it had to face the street - but we live walking distance to shops (think of the petrol saved on not having to get into the car), we've got clerestory windows on the west side so no afternoon sun issues, and we're assembling a collection of sails for the south side, where the deck is, to provide shade from the late afternoon sun. Oh, and skylights for the kitchen. No, not ideal. But the location is, and the designers have worked around the constraints of orientation. And that's reality for a lot of us.

If you search DIY banquette on Pintrest you’ll see instructions and measurements. Most are in inches but you can convert them. Could you measure the seat height of the chairs you are using with the table (you need the table first) subtract the cushion height and that will give you the bench height. It does depend on the height and weight of those that will be using it the most, to get the best fit.

i would probably try for at least 90cm but depends on the size and shape of the room, location of doors and windows and size and shape of other fixtures..can you post a plan of the room?