Roland, as a character, is best off focusing on himself up to level 50. Impact, Metal Storm, Fitness, Overload, Grit, Stat, Defense, and Quick Charge combine for a great overall buff for him and it is difficult to justify not maxing those skills out at 5/5.
Between Assault (Assault Rifles) and Scattershot (Shotguns), the latter is by far the better of the two and is simply an outstanding skill. However, that comes down to what you prefer and people that run Heavy Gunner might opt to select neither weapon class. In general, as Roland, you are almost always best off running a very offense-orientated class mod because the Scorpio Turret provides good defense.
Once you have all of the Roland-first skills, I recommend making sure the turret is available as much as possible. Having both Deploy and Refire at 5/5 might seem redundant, but it is not and goes a very long way in keeping Roland on his feet more as enemies will be more consistently distracted.
After that it becomes personal preference. I usually max out Barrage and Sentry and place one point in Guided Missile, Supply Drop, and Grenadier. All three of those skills provide good returns with just one point, with the first two not improving as much at 5/5 as you would hope. This approach tries to squeeze as much out of the turret as possible after Roland has been maxed out.
This would be an endgame Commando Roland.
However, if you do not like Shotguns, then you could shift the points elsewhere. I think Aid Station and Stockpile are extremely underwhelming. The former makes you camp out near the turret, thereby losing all of your tactical flexibility and Stockpile loses to a single point in Supply Drop on top of once again losing all of your tactical flexibility.
Also, remember that the turret can debuff most enemies by applying corrosive damage over time! This makes Roland better in a similar way to Axton’s Double Up!