Just Google the dungeon name and you should find some sites that include maps along with their runthrough suggestions and info on mobs and treasure. FFXIVInfo has maps and treasure lists. Here's its page for Sastasha, for instance: http://www.ffxivinfo.com/maps/sastasha-seagrot.php Eorzea Reborn, on the other hand, doesn't always have maps, but it has more info on the fights themselves and any special mechanics involved: http://eorzeareborn.com/sastasha-dungeon-guide/

I agree that running them as a DPS or healer doesn't really help you learn the map, because you end up just following the group rather than watching which direction on the map you're travelling. Your first few runs as a tank are bound to be a bit slower than tanks who've run it dozens of times. Despite the bonuses Roulette would give you, you might consider choosing the dungeon specifically a few times when you're trying to learn your way around it. They're easier to learn if you keep repeating the same one until you learn it, then move on to another. There'll be time enough for Roulette rewards once you're familiar with the route on all the dungeons Roulette can pick for you.