I'm really interested in what the different types of rotis you may find in India. Is the roti basically at a base flat-bread made with wheat flour and then basically flavored with any other flour. Off course you would then get different spices added to it, but what exactly is the difference between the various types of Indian roti?
Roti & chapatti are the same thing with a different name.
Both are made with only wheat flour (atta) & water - though some prefer to add a little oil, that's not really a part of the base recipe. If you add oil to the dough after formation, whilst rolling then folding you get a paratha instead. Milk & oil or ghee is going more towards a puri.
You can cook them in one of two ways. Dry-heat on a tawa or regular frying pan, then flame them, or just keep on the tawa. Personally I prefer flamed, but that's not too easy at home. The chefs I used to watch used huge tongs, like two wire table-tennis bats on a scissor to hold them over quite a wild flame. My gas range produces a very tame controlled flame by comparison & I have never been able to find those tongs anywhere.
The only other real difference, which may be area or even just family tradition related, is their thickness & pliability. My favourites growing up were always the ones that went soft & highly pliable after a few moments cooling; definitely best for picking up your food - we used to jokingly call them 'wash-leathers' but that was the type we liked & would return to establishments that could make them that way, rather then the dryer ones with a slight 'crisp' to them. Where I grew up most of the chefs were Bangladeshi, but I don't actually know if that variant is truly geographical.
I've moved away from that predominantly Bangladeshi-staffed area since my youth in Bradford & no-one around here (London) makes them that way, they're much more layered & dryer. Nowhere near as good imho.
Presumably, in the same way a plethora of various flavours, fillings & toppings have been added to the humble naan in the 40 years or so they're been widely available outside the sub-continent, you could add any other ingredient you like - but then it's not truly a roti any more.