How much carbon will be put out to create a vertical farm? Urban areas with soil and rooftops may be possible, but spiral greenhouse buildings with large window areas seem counterproductive.

No they can stick vegetation on the sides of buildings is all- think skyscrapers covered with moss. When they say vertical they mean it :) .

I've only slightly looked at it so I'm not sure what you could grow in regards to produce though.

Heating of the vertical building would be quite a carbon output.

check the site man, bio and photovolactic windows

No site is provided.  Temperature and humidity control take energy.  Vertical only becomes necessary when the population requires more productive land than the globe has available.

Well we're there Luke tbh. But if you look at the reasosn specified in the OP you're not really addressing them- Vertical gardens means more (good) food and local food for cities (no transport carbon). 

Its not a seperate building, its the walls of already established buildings. Bound to impove air quality too- I'd much prefer carbon being converted into grass on skyscarpers than wafting around in the atmosphere for god knows how long.

Oh and:

http://www.thegrowspot.com/know/f5/vertical-gardens-living-walls-53838.html

Could take some getting used to, but we'll manage.