I've worked on my share of roof top gardens as well, but never in as severe a climate as yours. I would beg to differ with Nandina on the suitability of a Japanese maple in the location as you've described it, I doubt it will ever look good. You don't say how deep your planters are, if you don't have sufficient depth and width of soil in these planters, anything that can't tolerate frozen soil at the roots will not survive the winter. That greatly limits the selection of woody or evergreen plants. In general, whatever you end up using, I'd suggest that your automatic irrigation system provide up to twice daily watering for a few minutes each cycle for best plant/root health. In general the deeper the soil depth you can provide, the greater possibilities for larger sized healthier growth. You might also consider using portable pots that can be set inside the permanent planters which would allow switching things out seasonally more easily If you're interested in red foliaged small trees, you might do better with Berberis thunbergeri cultivars or Cotinus coggygria cultivars as being far more sun/wind tolerant. Another cool looking accent shrub/small tree for you might include Poncirus trifoliata 'Flying Dragon' I'd suggest you use some hardy succulents in the mix such as Serum spectabile or S. rupestre Angelina, Sempervivums, grasses hardy to your zone. If you'd be willing to consider duoble potting your containers and bringing them inside in the winter, you could plant some truly sun/heat/wind tolerant plantings using architectural succulents such as Hesperaloes, Aloes,Agaves, Dasylirions, Echeverias, etc. These could thrive in the more temperate months outdoors and be brou__ght into a greenhouse or sun porch for the winter, and you could plunk into fall/winter seasonal accents in their place if you still needed something out there in winter, or maybe just park some cut greens and cut colorful branches such as Cornus stolonifera or willows for winter. I would stay away from any plants up there that can't stand up to the wind and hot sun and some drought stress. So no big or soft leaved plants that will wind burn.

With fast expanding urbanization, roof gardening is definitely an option. In Japan for example, roof top gardening is so widespread. In Singapore, they practice this also. One case in point is the roof top hydroponics garden of Changi Hospital, that supplies a large portion of the vegetable needs of the hospital. Singapore is much warmer than Manila. From experience and discussions with other enthusiasts using NFT PVC tube, I gather that the inside of the tube heats up a lot. Hence the solution becomes lukewarm and adversely affects the plants. What some do is to use white PVC tubes or wrap the dark colored tubes with foil insulation. According to them, the rise in temperature inside the tube is negligible. The foil insulation consists of a foam sheet (about 1/2 in. thick) with a layer of foil, as in aircon ducts. The tube is wrapped with the foil outside to deflect the heat of the sun. Another consideration for roof top hydroponics in the Philippines are the strong winds during the stormy season. The area is prone to storms. Preparations have to made for this. Given a chance I'd like to do roof top hydroponics, if I had the appropriate roof space.

One thing you would have to deal with is the extreme drainage. Water seeps out of/is wicked away by the cinder block, or most cinder blocks anyway, the $2 masonry blocks. Thus I think that growing a plant in that narrow cinder block column would not work well unless you do something to counter-act this, and even then I think that the long narrow column would be kind of hard for the plant to get used to. I want to try growing hot peppers in the blocks, because I am hoping they will serve as a good heat sink and help keep the plants warm. In my case though it will be just a single block buried halfway in the ground.

sierraeast - The views are somewhat subjective. The city/ocean view is on the west side of the property. The east, south and north sides have OK views, but nothing dramatic. The units already have lanais on the living floor not to mention an accessible rooftop deck. In a condo setting where people have no access to exterior living areas, I agree... a lanai would be preferred so people have some place to be outside while in or around their home. But in this case, people have a couple options to enjoy a little outdoor living. Also, the traffic noise can be loud during some times of the day and evening so I wouldn't think people would want to stand outside the lanai, especially in a bedroom. Believe it or not, most condo owners in Hawaii have their lanais enclosed if the governing association allows it. I guess if people want to be outside, they just go down the street to the beach : ) lorraineal - yes, I thought about that. I would think that people would clean the area as they would any other interior plant collection. From a cleaning perspective, having this exterior planter is no different than having a few plants inside your home. You have to pick up the leaves every now and then but in an exterior setting, this can be done less frequently than if the plants were indoors. The plants will be mostly accessible from a sliding door (center sliding door, similar to a french door so 50% of the area is accessible directly from the edge. The area is not large - only 26" deep, so it should be fairly easy to reach/maintain. I was hoping to get a few thumbs up... so perhaps my idea is baked.