More "suburban" than urban, perhaps, this greenhouse I helped my girlfriend build has been producing food, while she learns which plants grows well in it and so on. She's very conscious and careful about what she eats (much more than I am), and she really wants to be independent of the corporate food stranglehold.
Total cost was about $2K. One could do it for less, but she rightly insisted on using proper materials such as treated lumber and hardware etc. The specially-designed covering material came mail-order from a company in Oregon. The "temporary" structure requires no building permit, since its foundation is three heavy railroad ties basically just resting on the ground.
Its situation makes it like an additional room of the house, a pleasant one at that. Anyway, I want to share these pics, they might elicit ideas for others considering a greenhouse.
Two amateur carpenters construct a greenhouse abutting a patio door.The plan:

Prepared bed of sand topped with pea gravel, and three cleaned-up and shellacked railroad ties for the foundation:

All stainless steel hardware; the creosote in the railroad ties would eventually corrode anything else:



Piece of treated 2x10 forms a door sill and ties the foundation together:


2x4s are fastened to the house for attaching the structure. Front stud wall ready to raise into position. All fastened with exterior screws---no nails:



Roof beams: saber saw shapes the rounded ends, over which the plastic covering will fit smoothly:


Connected to the house & back wall, with various roof bracketry obtained at Home Depot (I think we spent more time at Lowe's and Home Depot than at the building site):


Side wall studs are measured and fastened into place:

Amazingly, everything is remarkably level and square for our level of carpentry skills!
Horizontal cross beams are 2x2s, to minimize light blockage, except for the 2x4s supporting the side windows:

We'll figure out the door later...

The back wall of the house leans in a bit, so this angle adjustment was made at the first side wall studs:


It might look like we did this in a day -- but it took
weeks, working on it when we had time.
The translucent covering material (has better light distribution than clear) comes on a large roll and is secured with cap screws:




Making the doors & windows was a small project in itself. These photos were taken months later, after it'd become a functional greenhouse:




A view from inside the house:
(The piece of machinery at left is a 100-year-old working platen press, on which she still does 'boutique' printing jobs.)
You like eggplant?



The gravel allows good drainage...

View through a side window:

Something is causing yellow spotting on the leaves here -- can't figure out what/why, but otherwise the plant is fine:


Here are some pics of her other garden efforts:
Grapes!

Beans! Veggies!


Deer cross through her yard a lot, the fencing around the garden keeps them from snacking on it.
Dangling CD discs, flashing reflected daylight, supposedly discourage crows looking for snacks.



Blueberries!


An apple tree is nice to have as well:

I didn't get shots (limited by power cord) of more berry bushes, and the hazelnut and pear trees, all of which she planted.
For much of the year, she grows most all of the food she eats. Which is pretty awesome.
Myself, I live in an old (1895) apartment building with a flat roof, I want to make a vegetable garden up there. The landlord said 'okay' but I'd have to install a secure access stairway, etc., so it won't happen very soon. But it's definitely something I want to do.