I really want to get ROA in dominion sometimes, but I feel it is not worth the investment unless you rush it. I tend to stay away from it for that very reason because i want to get a item that will reach its full effects without having to rush it. While i understand the reason they removed Warmogs was because of how much health it gave and Riot wants to avoid something like that, why not maker a cheaper/weaker item like ROA for just dominion?
Honestly it sounds like people are saying its good for mana and sustain in bot lane. Well here is my two cents.
If you want sustain in the bot lane you might as well save the Catalyst and upgrade it to a Odyn's later. I rather get a Catalyst and get a Rylai's, then upgrade the Catalyst to a ROA.
If you where to get ROA at 5 minutes in game and where to reach 15 minutes you would get 630 HP, 725 Mana and 80AP fully stacked. I think most people would rather take the Rylia's because that gives 500 HP and 80AP off the bat. It also gives a slow to all spells.
Now the mana part. In all honestly I never really build in tear (unless I am Urgot) or ROA for mana in dominion because I find that with proper mana management and making full use of health shrines I really never run low. I really never find myself running out of mana a lot in dominion due to Runes and Masteries I use.