Caesar's and Mandalay Bay are just a couple off the top of my head that have showers big enough for 2.Usually there is 2 or more shower heads.The review you read are you sure they were speaking about the size of the shower?
A look at urban dictionary gives a whole different definition I would not expect when the words roman showers are mentioned.

Try the Trump. The room I stayed in had a shower that will comfortably fit three people.  

From what I heard, you can get their rooms on Priceline with the search criteria of four stars and suite.

The Paris La Mans bathroom is so big you need to pack a lunch to get from the toilet to the shower.

I am a shower Goddess!  lol