I usually roll chars on 4 d6 taking off the lowest for 6 times, then place the results as i think best for the race/class combo at hand and in the end add the racial modifiers. I saw that usually PBP GMs want char built on 20 points, but if the result of the dices is within that limit but exceeds it with the racial modif is a hypothetic PC acceptable ?
For example, 9-9-11-13-14-17 are worth 20 points, but i had to add +2 or more.( of course with a -2 balancing it )
Racial modifiers are added after whichever method you use to generate stats (whether by rolling or by point-buy).
So, you first roll/buy, then you add racial modifiers.