AWhat kind of ratio do I need To make milk chocolate ganache if I have 200 grams chocolate do i use 200 cream? And so on Also can I add flavor to ganache?

I use a 2:1 chocolate:cream ratio for making chocolate when using dark chocolate.  Milk chocolate has a higher milk content and so you would need a higher ratio, maybe 2.3:1.

However, saying this, I live in an area very hot and humid in summar and during those times I alter my ganache recipe to 2.3:1.

All the best

ADo I add. Anything else or is it just cream and chocolate? I live in a hot Country Too its not to bad. At the mo tho but last time I made ganache it didn't turn out to well.

I always wondered - does the ratio have to go by weight? Meaning I have to weigh out the cream too? I'd normally measure chocolate by grams and cream by mililiters...

1 ml = 1 gram.    500 ml of cream is 500 grams.  Easy!    After completing the ganache, before it is cooled, you can add in all kinds of flavoring if desired.  Extracts, liqueurs,  even seedless preserves like raspberry or strawberry.  

AI put the ganache on the cake today cake it came out lovely. I just done all the smoothing with the hot Water and spatula looking good :-) I'm Really pleased With myself. Just the fondant icing to do now. :-)

There is nothing extra to add when the weather is really hot, just adjust your ratio - more chocolate less cream.  I know when it is super hot and humid even a ratio of 2.3:1 chocolate:cream isn't enough to ensure the ganache will set firm enough to use under fondant icing (or for anything other than chocolate sauce on icecream!).