Swashbuckler battlemaster multiclass worth it?

If so, how to build it?

Sure, it can be pretty good.  You need to decide, though, whether you want to prioritize doing more damage or getting more access to useful skills. 

The Swashbuckler uses the Rogue chassis, so if you go Swashy first, you get more skills and you use them earlier.  Your damage will probably be higher from levels 1-4, but will probably drop off a bit compared to a Battlemaster after level 5 or 6.  If you go this route, probably pick up at least 1 level in Fighter after level 4 so that you can get a Fighting Style.  

The advantage of going BM first is that you get maneuvers earlier, which gives you more variety in combat.  If you take this route, go BM until at least level 6 for your second ASI and 2nd attack (at 5th level).  Having your earlier levels in BM also makes your character tougher to kill in melee, which is fairly important for a front-liner..  

A core problem with this concept is that you can't actually achieve that combination before level 6, and if you rush towards it you wind up with zero ASIs at level 6, which is not optimal. In general I would structure my progression as one of the following

• 4 levels rogue to start with, then 5 levels fighter, then back to rogue (you might take a 6th level fighter for the ASI at some point, but not until late)
• 1 level rogue to start with, then 1 level fighter, then +3 levels rogue, then +4 levels fighter, then back to rogue (as above)
• 1 level rogue to start with, then 6 levels fighter, then back to rogue.

In terms of build details:

• I'm not a fan of two weapon fighting; you've got other uses for bonus actions (cunning action is pretty awesome). Consider rapier and shield with dueling or defense fighting style.
• Reaction attacks are awesome on rogues, because sneak attack is per turn, not per round. Consider Sentinel. Or take martial maneuvers such as brace or riposte.
• Expertise plus Commanding Presence can give you persuasion or intimidation checks that are competitive with bards.