[Swanny]

Any roof that has a guttering can be used to collect rainwater.
I would recommend getting some water butts and placing them under the downpipes from the gutter.
We used to make similar to southern cross water tanks and feed them from either church roofs or just a few sheets of corrugated iron. You can either link the butts together or just redirect the flow to each. I recommend using some type of cover that lets water through but stops crap like leaves, flies etc from contaminating the water. You can get a membrane that stops weeds from growing in your garden that is ok for this.
Hope this helps