You'll really get the best out of this exercise if you try it yourself. Why don't you post what you're thinking and we can help?
Hint: Do you think this makes more sense top-down or bottom up?
Remember that there's rarely a "best" answer with market sizing. What's important is that you break down the problem the way it makes sense to you. Importantly, break it down so that the assumptions you make are the ones you're most comfortable in.
For example, do you know all the major brands? Great go with that. Do you understand all the segments of that country's population (either age or wealth or job breakdown)? Go with that. Do you know the total market size of a similar industry? Then break it down that way.