Most roofs are suitable for solar PV. However, roofs that are overly sloped or complex (e.g. with many build-ups that could cast shade on the PV system or roof with many small patches rather than one single large roof area) would not be the most ideal for solar PV installations.  You can refer to this FAQ outlining a list of vendors you can reach out to in assessing the suitability of your rooftop for solar PV installation. To get an impression of what types of PV systems are installed in Singapore, you may also check out some of the existing PV installations on the National Solar Repository website.