Rooftop gardening is nothing new. City dwellers have been tucking plants on roofs and fire escapes for generations. Even green roofs, roofs covered with soil and plants, have been around for years. It seems no matter how much land a gardener has, we always seem to be looking for more space, and rooftop gardens of all kinds are gaining popularity in both residential and commercial sites.

There are plenty of good reasons to consider a rooftop garden:

• They make use of unused or underused space
• A garden beautifies an eyesore
• They can provide privacy
• They can be extremely environmentally friendly
• There is usually good sun exposure
• No deer

If you’re considering a rooftop garden, there are a couple of directions you could go in. Fully planted green roofs, where the roof is covered with soil and the plants are in the ground, make great environmental sense, but they are too difficult for homeowners to undertake on their own. Green roofs can easily top 100 lbs. per sq. ft., before adding people. You would need to need to hire a structural engineer or architect to conduct a structural analysis and probably a professional company to install it.

The easiest and most personal approach to rooftop gardening is the use of containers and raised beds. You can create any style of rooftop garden with container grown plants, from a few simple herb plants to a formal, elegant potager.

Containers are perfect for rooftop gardens because they are light, portable, flexible and affordable.

While caring for container grown plants on a rooftop is much like maintaining containers on the ground, there are a few rooftop idiosyncrasies to consider before you start hauling your pots outside.

• Permission: First, check with your landlord and/or building code. Questions about accessibility, building height restrictions and fire regulations can prohibit any type of roof use.
• Structural Integrity: Make sure the roof can hold the load. Get a licensed pro to do this. Soil and pots are heavy to begin with and will get heavier as the plants grow. If you’ve ever tried to move a pot full of wet soil, you know how much weight water can add.
• Access: How are you going to get your materials and supplies in and out? If you live in an apartment, make sure you are allowed to use the elevator. Some municipalities require multiple access/exits and possibly exit lighting, fire alarms and emergency lighting.
• Water: Will you be able to run a hose out to the roof? Watering cans can become a nuisance and containers require a lot of water. Consider installing a rain barrel and drip irrigation.
• Sun Exposure: Are you shaded by nearby buildings or the terrace above you? Even fun sun can be a problem when plants are sweltering on top of concrete.
• Heat: Besides the sun beating down on the roof, there is ambient heat being reflected from the roof surface, surrounding buildings, street cars and metal exhaust and utility structures. You will probably want to provide some sort of shade, if not for the plants, then for you.

• Wind: Wind can whip down straight urban streets, especially on high-rises. You may want to consider some type of wall or fencing. If so, you will probably need to check your building code again for required heights and structural stability. This is especially important when building safety barriers for kids and pets.
• Privacy: Most rooftops are surrounded by neighboring buildings. If your rooftop garden will be in full view, you may want to plan for screening. You can plant a hedge of evergreens, run vines up a trellis wall or simply tuck under an umbrella table.
• Electrical Wiring: Electricity isn’t essential, but it sure makes things easier. If you are planning on enjoying your garden at night, candles aren’t the best lighting for weeding.
• Storage: There’s a lot of paraphernalia associated with gardening: tools, fertilizer, compost, buckets. Space is limited on a rooftop and it’s hard to camouflage a storage area. Shelves will suffice. Some rooftop gardeners opt for narrow closets. Another option is bench seating with built in storage, to do double duty.

• Cost: Last but not least, how much are you willing to spend? You can start small and add on, buying more pots and plants (and soil) as you go. The real expense comes when you want to start hardscaping and building on the roof. Laying tiles or stone, building raised beds and boxes, adding lighting and furniture can all start to add up. Plus, you may need more structural work to support them. – source