League of Legends (LoL) Question: Pantheon Build

As it seems like you're talking about laning Pantheon because you aren't mentioning any jungle item. When laning I don't recommend you building Mobility Boots is not being able to roam a lot especially when playing mid lane. One of the core damage item combination would be The Brutalizer + Last Whisper. The best lifesteal and sustain item is definitively Ravenous Hydra. You can build an early Tiamat for the wave clear if not being in need o building LW right after Brutalizer. Randuin's Omen and Banshee's Veil are great defensive options. Sunfire Aegis is supposed to be built earlier on on bruiser-type champions and therfore not recommendable.
Bloodthirster isn't a complete no-go but it's not as great as it's used to be on Pantheon I guess. Infinity Edge would be a niche pick option as a further offense option.

Build for mid lane: Mercury's Treads/ Mobility Boots, Black Cleaver, Last Whisper, Ravenous Hydra, Infinity Edge/ defense item and defense item (consider Hexdrinker in lane when suffering from the enemy APish opponent)

Top lane build is similar but you consider building more tankier at all and possibly early on.

First off, where are you planning on playing Pantheon in? Lane or Jungle? And just write down the build in your question comment instead of tagging items.

clearly your build should be a complete rune page of attack speed runes and then buy a dagger first item. then practice soloing dragon at level 1 until you can do it

Panth is an early game champion so rushing last whisper generally isnt a good idea. I would recommend rushing bloodthirster or ravenous hydra or maybe infinity edge first instead because overall it will give you more damage early. Also when in doubt, get a brutalizer. This crushes people early on due to low amounts of armor.