Ideally, the panels should face 15.87° (latitude of Thailand) South if you're trying to maximize your average power output throughout the year. If you needed more power during different times of the year, you may want to consider deviating from this. For example, Thailand is hotter when the sun is directly above (Late April/Early May) and so you may need more air conditioning power at that time and would have your highest power output at that time if your panels face directly up at 0°. The consequence is you'd have less power available during the "winter" due to the sun's incident angle being as high as 39.37° around Dec 21st but if air conditioning is your primary cost, this trade-off might work.
The roof facing East and West is an issue I have. Putting panels on the East and West side of the roof to cover morning and evening would not be the most efficient. Ideally, you would use brackets to level the panels out and face straight up (countering the roof pitch) and then tilting 15.87° South for the best average output, and you should avoid the ends of the roof to avoid shading of the panels during the start of sunrise or end of sunset. There isn't a lot of power to capture during these high sun angles anyway, so it's not something to get too crazy about. And it may be easier to just go with more panels flush to the roof than to deal with trying to install them in a way that would counter the slope of the roof. So if you have the roof space, it's probably best to just do more panels.