Monster roles may also be changed a bit in 5e. I hope, 5e has assigning monster roles just the other way around (actually I do design them that way):
IMHO you should assign:
AC, HP, Defenses, Attack bonus, Damage expression ranged, damage expression melee, consult a chart with appropriate level for the monster. Dress it up with PC advancement rules, and you get a certain number of hp, armor etc., look at the chart and know how much xp it is worth.
Guidelines should help:
Just say: here are 5 possible combinations that result in balanced monsters that can fullfill a cetain combat role very well: brute, lurker, skirmisher...
i hope you get the point.