Hi, these are just items I like to run. Im not a high elo player so take everything with a grain of salt. I will still try to explain my thought Process with each build.

I think its pretty Obvious that PTA bruiser is briars strongest build. PTA is stupid right now and her synergy wtih BORK is absurd. Building Cleaver second is very important due to the tankiness it gives you as well as the hast. You can also stack it very quickly, and it stacks with your Q shred. The rest of the build is simply playing to be hard to kill while destroying everything in your path. Briar is in general a very strong early game champ. With any build, play to that strength, and try to end games early as you don't scale very well compared to other champions.

Lethality does stupid damage once you get your items. with the combo of LDR+Collector with your first lethality item makes you deal close to true damage to people not stacking armor, and deal nuking amount of damage per auto. The only problem with this build is you get nuked yourself. Against hard CC and knockbacks like alistar, vayne, or janna you can't really do anything to stop yourself from getting annihilated. This build can be very fun however against low mobility carries such as jinx or jhin where you can simply 1 shot them. Catching tankier enemies in side lane is also an option if you use your ult due to AD converting to resistances.

Short answer to this question, its fun. AP is silly as briar is a very auto attack reliant champ and AP doesnt really help with that. The big upside of AP is the dopamine hit you get when you slam someone into a wall for 1500 damage instantly killing them. This build is really just for fun but if your team need magic damage and you know how to use your E correctly it can deal massive damage. Your Q plus your red jungle pet help you land Es very easily and if you know how to play around walls you can get knock ups fairly easy. your Q also shreds MR and has a 60% AP ratio meaning it can dish out some great damage once you get to around 3-4 items.

Don't im bronze, but this is what i've learned after playing briar for a while. I love this champ but I used to play shaco so I love playing champs with very vesatile builds and I think briars are much weaker than AP shaco vs Crit Shaco vs Lethality shaco but they're still extremely fun.