Guide:Sharpshooter
This will be a guide for a build that focuses on dealing 
Physical damage from a distance.
Core components for this build include:
- Any kind of Hand Crossbows in each hand
- Sharpshooter feat
Sharpshooter provides additional damage for a penalty to accuracy. Attacking from the distance helps to mitigate the accuracy penalty (high ground, hiding) while Hand Crossbows allow to use bonus action to make attacks. Which the bonus damage from Sharpshooter this additional attack more than compensates the fact that Hand Crossbows have less basic damage compared to the Heavy Crossbows.
Having minimalistic core this build allows many approaches from the class perspective. The most notable options are:
Battle Master fighter
Hunter ranger
Gloom Stalker ranger + 
Assassin rogue
and 
Thief rogue should also be viable choices (that I have not tested yet)
t.b.c.
Other class options
Beast Master: overall a viable alternative for the 
approach. This subclass does not bring improvements to the range combat hence putting the option into "Other" section. Still beasts are strong and overall Beast Master version will bring both firepower as well as survivability and flexibility to the party.
Champion: an alternative option for the 
approach. Main benefit of this version is an improved critical (equivalent to about 5% overall damage increase). For a ranged build a Champion is more interesting than for a melee one - there are a lot of ways to guarantee crits for melee strikers in bg3. Still Battlemaster manoeuvres provide a comparable damage increase together with a ton of utility and flexibility.
Do note that this subclass makes more sense if you try to minimise amount of long & short rests.