*pops up*
As has been said you can indeed keep robos in pairs and groups very successfully, what is most important to remember is to only keep as many as you have the space, means, and time to keep separately though, as there are never any guarantees they will stay together and live peacefully.
Most pet shop robos will be seven to eight weeks old when you bring them home, the same with breeder robos. I let mine go at eight weeks to their new homes, but I will have been monitoring them as a pair in the cage they will be going in for two weeks beforehand, not something that happens with a pet store.
The problem that most often arises is that people bring their new little fluffs home right at the time they charge head on into puberty as the hormones really start flying about at eight weeks, and often don't completely settle till over six months. There is of course no warning from shops about this, so time and time again people find themselves with little robos at war and have no idea what to do.
Cage set up has been discussed so I won't recap, I wouldn't advise following any of my set ups for an adolescent new pair, as Nikki says I use a different dynamic due to having babies to put in with older relatives, if you have a single robo though platforms and levels are great.
I have had many beautiful happy boy pairings over the years, as well as a group of eight boys all together, but I will say that girls really are on the whole easier. They aren't as worried about being dominant, there is no testosterone flying about, and if they do fall out, they are so much easier to put back together again peacefully.
So decide whether a pairing is for you, if not, consider adopting one of the many little ones out there that are already alone, and you can make then the most amazing set up without worrying about arguments
I would say though that if you are offered a pair of robos that are under six weeks old do not take then as they should not be going out to new homes at this age.