How to build a garden on a roof made of galvanized iron

The Garden I built on our Galvanized Roof 

My special bonding with plants started when I was in grade 6. The unpaved roads of my hometown were lined with evergreens laced with colorful flowers. On my way home, I would get a cutting of each variety per day. Planting those cuttings in  tin milk cans filled with soil readily lined on top of 4 old logs, formed into a square, was such a solemn ritual for me. My days were filled with expectations, eagerly looking forward to my rendezvous with my cuttings as they sprout into robust plantlets. Witnessing flower buds bloom into full glory amazed me no end: such phenomena of life made my supposed to be growing up pains pass unnoticed.