I rent a one room apartment - 19 sqm. Kitchen, living and dining room all in one. Thank god the bathroom is seperated. It's just me living here and it's all I need (I'm a student after all). I don't have a garden. I have a large park with a lake about 300 meters down the road though, and a balcony, which has about half the size of a washing machine. Good enough to stretch out my legs
And I don't think there is a "too large" for either house or lot size. If somebody needs a garden of the size of two football fields, well, that's his personal decision and as long as he can afford it, I'm fine with it. Not my business.