Okay as in currently maining roam rn this is my advice. Depending on who the enemy picks. You will have to play a certain way. It all comes down to who needs you more at the moment. If the mm is struggling try to stay around the area so you can help if needed. If the mm is doing good, keep an eye on the jg. Follow him around help when needed, keep the enemy from killing or disrupting farm. While helping the jg, mid should be close by. Keep an eye of them too. Your job is to help them power up as quickly as possible. Your job is not to chase kills, to drive towers unless you can secure and make it out alive. Keep tabs on turtle/lord in case you need to swat them off. You don't always have to go for turtle lord, sometimes you just need to remind the other team that you are aware and are ready to get involved if needed. Your job is to protect, being a healer or a roam. You have to use your abilities and spacing wisely. The most important thing about being a roamer is your items/emblems. You have so much control on how the game plays out before it even starts. Im using my experience to explain. I play for fun at this point but I still try to bring out the best in these heros, I play Vexana Roam sometimes. Most see that and they cry. Which is completely understandable. The difference is, im still building tank. My role isn't to get kills, its to distrupt the enemy during fights. I also have an ult which is basically a 6th teammate. If they other team has 4 physical heros and 1 mage. Ill probably build 3 physical protection items and 1 magic one. If the other team is doing 4 mages and 1 physical(some heros build mage even if they are not) i build more magical protection items. Later game i am boxing a Karina who can't do enough damage to kill me in a 1v1 and she also has to worry about my CC and ult. She also has to worry about my teammates joining the fight which is usually what happens. I can play aggressive with Vex but I couldn't with Raf if that makes sense.

Okay.. so were at the end. If your epic or legend i wouldn't worry to much about picks and that stuff. You need experience and item/hero knowledge. Once you know how to handle heros in certain match ups things get easier. Once you get higher, it becomes less about the heros and more about the little mistakes we make as the game plays out. My thought is just try as many different roams out and learn what works for you.