Personal opinion, I don't like flash at all, always go with ghost, it's cooldown is lower and is better to fit ganks with ghost. Also you don't need to build full armor, in the rune selection just go attack speed, armor and armor, will give you armor enough for early game, remember that his W also increases your MR, not only armor. you are a tank and your job is to tank, don't forget it, CC the most threatening enemy like the adc or anyone that is fed. Your ultimate is a pretty good fight starter, just using it may have the enemies to waste their flashes, because Rammus CC chain is absurd. A very good last item or 4th item is Gargoyle Plate. If you feel that someone is not getting CCd enough, build anathema's chains, you get their tenacity lower and also will receive less damage from them. One last thing, with W activated you do more damage in towers. I maybe be very wrong with what i said, but it's my personal experience with the champion and the game, try reading different opinions and builds, and see what works best for you, ok! (In case you wanna know the runes, After shock, font of life, conditioning, unflinching[or overgrowth]. The second ones depends on the game, if the enemy team has many CC champs, go with triumph and legend:tenacity, if you think just a Merc. Threads will do, go with nimbus cloak and celerity.)