Different areas have different types of flat breads, but is there any meaningful difference between them? What is the difference between pita bread, roti, naan, and tortillas? Is it just different types of flour used in each case or is there any other differences in texture and taste.
All of the 'flatbreads' you describe are generic terms which encapsulate many, many variants (e.g. there are dozens, if not hundreds, of types of 'roti' from cultures across the globe). So I'll have to make some assumptions about exactly which type you are referring to.
Pita These are typically a two-layered flatbread, formed when a flattened dough piece separates into two distinct layers during baking. That pocket formed during baking is a key difference from the others that you mentioned. Pita are a yeast-leavened bread, something which would greatly impact the texture of the bread (i.e. Leavening agents are used to achieve a light and crunchy texture and to increase the volume and porosity of bread crumbs). Depending on the leavening process used, this could also impart a slightly sour taste to the bread. This family of breads could encapsulate 'pita pocket' style breads, the style of bread used in Greek cuisine to wrap Souvlaki, and numerous styles of Arabic bread.
Roti There are so, so many variants of a 'roti'; from Malaysian Roti Canai to Trinidadian Roti to Sri Lankan Coconut Rotis (just to name a few). I feel like the differences between these types of rotis would be a big question in itself, as they range from flaky, oil-rich doughs, to filled breads, and more. The wikipedia page for 'roti' might provide a jumping off point if you wish to explore some of the common types. There are so many styles and base ingredients here that you'll find such a wide array of flavours (from different base ingredients and flavourings) and textures.
Naan Again, there are many variants of naan, but I'll focus on what I think is the most commonly known type, i.e. Indian naan. These are another leavened bread, with a distinct 'bubbly' texture, cooked in a very hot Tandoor (a deep, cylindrical oven typically heated via charcoal or wood). This cooking method is a key difference from most 'roti', which are cooked on pan or griddle-like surfaces. This cooking technique will impact both flavour (imparted from the oven) and texture (an entirely different cooking environment is created). Milk or yoghurt is often used in Naan dough to give it a softer, chewier texture than many of the other bread types you have mentioned.
Tortillas Again, lots of types, so I'll talk about corn tortillas - the type common in Guatemala or Mexico. These are made from Maize (i.e. corn) that goes through a curing process to create a dough called Masa. This dough is then pressed/rolled out thinly, and cooked on a 'comal' (a smooth, flat griddle). It goes without saying that these naturally taste wildly different from the breads mentioned above because they use a completely different base (corn vs. other grains). And even then there are huge variations amongst corn tortillas (Mexico produces 42 varieties of maize). The three most common types of maize are white, yellow, and blue. Personally, I find the differences between these types of maize quite pronounced - I find blue maize to have quite a floral flavour. A good tortilla is typically slightly puffy when fresh cooked, and stays pliable and a little stretchy. You should be able to taste the fresh corn.
As you're probably sick of me saying throughout this answer, there are so many types of flatbreads, with a myriad of interesting flavours and textures to try. Go try some out and see! The comment above by dbmag9 that links to Wikipedia's lists of flatbreads looks like a great place to start.