This would be a Revenant Blade build using a half-elf variant (variant Human)

You are descended from a master of the double-bladed scimitar, and some of that mastery has passed on to you. You gain the following benefits:

• Increase your Dexterity or Strength score by 1, to a maximum of 20.
• While you are holding a double-bladed scimitar with two hands, you gain a +1 bonus to Armor Class.
• A double-bladed scimitar has the finesse property when you wield it.

Which offers a nice reliable high damage (2d4) finesse weapon with a 1d4 BA attack

Variant Human (rev blade)

16 16 16 8 8 8 (for 17ac)

1. Rogue 1 - athletics & stealth expertise, 1d6 sneak attack
2. Barbarian 1 - Rage & Unarmored Defence
3. Barbarian 2 - Reckless attack, for permanent sneak attack
4. Barbarian 3 - Bear Totem Barbarian
5. Barbarian 4 - +2 Str
6. Barbarian 5 - Extra Attack
7. Rogue 2 - Cunning Action a bit less useful for this build
8. Rogue 3 - 2d6 sneak attack and Phantom Rogue for Wails from the Grave (half sneak attack against second target)

Quick damage check, is three attacks:

5d4 +3d6 +6 rage +12 str

43 damage if all hit which is likely with advantage. But much better than the damage is the defence and skill versatility - but sadly you kinda have to sacrifice all mental stats for that… what do you think? What would you change?

Revenant Blade prereq is elf.  No half elves allowed.  But I am a DM who wouldn't mind it open to everyone since martials need more fun weapon options.

Quote from Elfdope >>

Revenant Blade prereq is elf.  No half elves allowed.  But I am a DM who wouldn't mind it open to everyone since martials need more fun weapon options.

The Custom Lineage option may help persuade a DM also that you are fully an elf, just of a different lineage - then you could start with a 18 in strength with point buy, but then a 14 or 15 each in dex and con

Its been previously stated by Crawford that Custom Lineage does not make you eligible for any racial feats just because you say you are that race.