Gung Fu?
Start Fighter for the proficiencies. Then take 3 levels and choose Battle Master. You'll gain the following class features that recharge on a short rest:
* Action Surge - In the first round you can Hex a target then make 4 attacks.
* Fighting Style - TWF or Duelist are both good for damage; you can Hex in the 1st rnd then draw a second weapon if you want to be a TWF
* Maneuvers - Disarm, Evasive Footwork, Riposte
* Second Wind - Self heal for 1D10+3
The next 6 levels will be Warlock with Pact of the Blade. What kind of character do you want?
If you want to be like a scrappy, tricksy Rogue I'd suggest Fey Patron:
* Misty Escape - turn Invisible and Teleport away as a reaction (recharges on short rest)
* Fey Presence - mass charm/frighten (recharges on short rest)
Cantrips:
* Chill Touch - target cannot heal or be healed for one round; this is how you can assassinate certain creatures
* Poison Spray - alternate damage spell; save or take 2D12
* Prestidigitation - you're not a spell caster without this spell
Spells:
* Armor of Agathys - good damage shield with no concentration; increases with level; 15 temp hp; and does 15 cold damage when attacked in melee; increases with level
* Blink - good defensive spell with no concentration
* Charm Person - affects 3 targets at this level
* Faerie Fire - advantage for you and allies
* Hex - extra damage is good
* Hold Person - you will be able to target two creatures, and then butcher them
* Mirror Image - no concentration, decent defensive spell
Invocations:
* Thirsting Blade - two attacks with pact weapons
* One With Shadows - Invisibility in dim light or darkness
* Mask of Many Faces - Disguise Self at will
Make him a 1/2 Elf for the boost to Dex, Con, and Cha, not to mention bonus skills, bonus languages, and Darkvision. Take the background Street Urchin for access to Thieves' Tools and other Thief skills. Start as a Fighter for a good spread of Saving Throws (prof in Str and Con, high stats in Dex and Cha) making you durable in several areas, and high starting hit points. Also, prof in Con is good for concentration saves.
You'll have a character that is good in and out of combat with a wide range of spells and abilities, does good damage, and has some durability.