For example, Roberto or Rojo. I asked some of my friends who are native Spanish speakers. Some say they do not roll it at all. Some say they do slightly, but not as strong as 'rr'. I googled it and apparently it needs to be rolled. I am confused. Help.
All countries use both the /r/ and /ɾ/ phoneme. Not all countries realize them, respectively, as the roll/trill [r] and the flap [ɾ] (for Puerto Rico for instance you often get /r/ as [h] and /ɾ/ as [l]), but whatever sound is used in the word perro /'pero/ will match a word starting with r-. You should not ever hear the sound used in the word pero /'peɾo/ at the beginning of the word.1
It's only written with a single R because there's no word on Spanish that begins with the sound made in the word perom thus it was a seen as an optimization (compare to L and LL either of which can begin a word). Note that if you add a prefix, the other R reappears to indicate the original trill: rojo /'roxo/ and infrarrojo /infɾa'roxo/ (not infrarojo /infɾa'ɾoxo/), romper /rom'per/ and corromper /korom'per/ (not coromper /koɾom'per/ ).
1. It is possible that (a) there is some dialect of Spanish where this is not the case, but I am not familiar with any, and that certainly doesn't apply to any of the major dialects —Mexican, Caribbean, Rioplatense, Andean, Peninsular— or (b) that someone has a speech impediment, in which case we're no longer talking about common speech.