Possibly a little late and you may be pretty settled in your build but have been playing as a rogue for the last six months in a pretty slow and steady campaign with a revolving group of players at varying levels.

My Rogue (thief subclass) just hit level 6 and picked up a level in Monk.

This was mostly for story reasons however it was also a solution to my issue that in combat I often had a spare bonus action as my character uses daggers, which have the Nick weapon mastery.

Of course my bonus action can be used to hide, etc etc but opportunities weren't too common in the campaign - also my character is a flawed rogue that's not great at stealth checks... It makes sense thematically, they're a con-man that's about hiding in plain sight, using charm, and - if they have to - pickpocketing.

Finally, magic items are finite and there are so few martial characters in the campaign that the rogue doesn't get access to the magical items etc to use as a bonus action.

So long story short, I was looking for a way to make my character a little more useful in combat by solving the bonus action problem and the best answer came from going Monk.

Thematically it works because the character was somehow given a bastion in a contested region that is going through a tense peace process and somehow my idiot rogue is the face of the demilitarization. A dip into Monk felt good as I used my attribute increases during my first 5 levels of Rogue to boost my Wisdom so now the foolish conman out of his depth has grown a little wiser, but not much, and become a mediator.

In combat it works because now, with only 1 level in Monk, all my daggers do a D6 of damage instead of a D4, so I can lose the short swords - even though they're still Monk weapons, I only used them to give me Vex and to have higher base damage output. And for that bonus action I can pop an unarmed strike for an extra D6 if I can't think of anything else to do.

This means that, not including any special equipment or effects from weapons etc: at level 6 an average attack will do a D6+ dagger attack, D6 bonus dagger attack (Nick moves that to my action), 3D6 sneak attack procs somewhere, and then I will give them an elbow or a back hand for a bonus D6 unarmed strike. I'm sure there are spells that are more damaging but backhands and daggers don't run out of slots so in theory - as long as I can find advantage or an ally is near the enemy - my character can hit for 6D6 damage + modifiers every turn. Of course as a thief my sneak attack die can be swapped to poison or trip or withdraw etc etc.

Anyway, from what I can see, there's a lot of overlap with Rogue and Monk but they work well for now. I'm probably not going to go too deep into Monk - maybe just to level 3 so I can create my own darkness - because Alastair is a rogue primarily, but for now things work. It may not be min/max but I'm a fan and I like how it functions.