How many types of Roti are there?
Roti &amp; chapatti are the same thing with a different name.
Both are made with only wheat flour (atta) &amp; 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 &amp; 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 &amp; 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 &amp; pliability. My favourites growing up were always the ones that went soft &amp; 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 &amp; 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 &amp; no-one around here (London) makes them that way, they're much more layered &amp; dryer. Nowhere near as good imho.
Presumably, in the same way a plethora of various flavours, fillings &amp; 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.