The following is from the files of online seed catalog "Burpee's".
These are "winter vegies" that we can grow on the roof:

Leek
Of the onion family, leeks and chives are best for winter hardiness. Both should be sown in late April or early May. Leeks, if spaced 6" apart in rich soil, will produce 1-2" diameter stalks of mild, onion-like, but distinctive flavor. They usually survive without protection until about the end of December and sometimes last throughout the whole winter. Chives are useable well into November. They put out new shoots early the following April.


Turnips
Turnips and Rutabagas are old standby winter vegetables. Rutabagas are somewhat more cold-resistant than turnips. Sow rutabagas the first week in August and turnips the last week in August for best results. The soil reaction should be close to neutral for best flavor. Sow thinly or thin to at least 4-6" between plants. Purple Top is the best turnip for fall use.


Carrots
Beets and carrots will usually last well into November even without covering. Both can be buried in a well-drained location and used until spring. The Lutz Greenleaf (or Winter Keeper) type of beets will reach huge size and still remain sweet and tender and are, therefore, strongly recommended for winter use. Goldinhart (or Red Cored Chantenay) is probably the best all around carrot. Sow both from July 4 to 15th. Neutral soil will produce the best flavor. Thin carrots to 2" and Lutz Greenleaf Beet to at least 6 inches.


Kale
Kale, Collards, and Brussels Sprouts are excellent leafy vegetables for the winter garden. All can stand short periods of cold as low as 10 degrees F with improved flavor. They can often be harvested until the end of the year-- sometimes even later.

Kale and collards can be direct seeded about July 20th.

Brussels Sprouts had best be started in a flat or seedbed about June 1st and transplanted to stand 2 feet apart in wide rows. In late fall or early winter the leaves can be removed from the stalk and the whole stalk with its sprouts can be hung in a cool dry cellar for late winter use.


Cabbage
Cabbage is somewhat less hardy. The red and the Savoy varieties are generally better for winter use. Culture is practically the same as Brussels Sprouts. Sow during the last week in June. Don t handle the heads while frozen. Wait for a thaw, then harvest.


Broccoli
Less hardy members of the cabbage family are broccoli, cauliflower, kohlrabi, and Chinese cabbage. All will usually yield into late November but not much longer unless covered with straw or sash. The individual plants which last longest are, of course, those with the best natural covering of foliage. Handle cauliflower the same as Brussels Sprouts and cabbage. Sow in early to late June depending on the variety.

Broccoli, Kohlrabi, and Chinese Cabbage can be handled the same as kale and collards. Sow broccoli in mid-July and thin to 1-1/2 feet. Sow Kohlrabi in the first week in August and thin to 1-1/2 feet.

Other vegetables that will usually produce into the middle or end of November are:

Spinach
Spinach (sown about August 25),
Swiss Chard (sown in mid-June) and Parsley (sown in late April or early May). A single sash supported by plants or a ridge of soil or bales of straw can often keep parsley in useable condition through half of the winter. Mats or old carpets on top of the sash will prolong the harvest still further.

Unless the winter is unusually severe, many of these crops will put forth vigorous and tasty new growth early the following spring.