Hi Mark,
Researching a name like Roberts is really quite difficult unless you have specifics to work on. Roberts is most popular in Wales, and is often a result of the patrynomic system. For example the name Probert, may be a contraction of ap Robert, ap being Welsh for son of or belonging to, hence son of Robert. With the English domination of Wales, certainly since the days of King Henry V111, names which were with pride were remembered and recited through generations were often afforded surname status when the authorities simply added an 's' thus Mark son of Robert son of Rhys son of Llewellyn could become simply Mark Roberts. Indeed the further you try to go back the more difficult it becomes. I've managed to go back to about 1770. But only because I became aware of where my forbears lived or were born. Beyond the 1840's this information is vital if you want to trace parish records.