A completely arbitrary series of estimates (guesses) follows. Based on this site  http://www.fao.org/docrep/009/a0310e/A0310E07.htm there are about 700,000 sq km of urban space on earth, which represent about 50% of the population. Assuming rural populations use less ‘stuff’ then say the total human occupied space is about 1,000,000 sq km. Taking a suburban setting as being ‘average’, and assuming half of the area is green space, that gives about 500,000 sq km. If all the man-made objects (housing, roads, etc) were flattened, lets assume a layer 1 metre deep (Convenient figure picked out of the air). That gives a volume of 5 x 10^11 cu metres, which would create a sphere with a diameter of ~~10,000 metres. 

This could easily be off by an order of magnitude: if anyone would like to find better estimates, I would be interested to see them.