The ideal for most fighters is 3 damage, 2 defensive, 1 slot for boots (technically a defensive). If you're building only a single damage item, then you're no longer playing them as a fighter, but as a tank. 1 damage, 4 defensive works for early game Fighters that transition into tanks due to lack of late game scaling like Renekton or Darius, maybe Rek-sai depending on how you want to play her (I usually end up with at least 2 damage items, and one off-damage like Sunfire), but that isn't the norm for fighter's like Wukong who have excellent scaling.
If you want an average, competent build according to players that know what they're doing, you can check sites like champion.gg that give you an aggregate build based on what players Plat + use. Wukong, for example, has Hydra-> Black Cleaver, Merc Treads, Last Whisper, Randuins, then either Banshee's or GA. Though what you build is always situational and can fluctuate based on your and the enemy team, this is a pretty fail-safe standard you can use.
There may be certain instances where, due to poor Champion Select communication, you end up playing a champion like Wukong when your team doesn't have a dedicated tank and you have to fill that role as best you can. Not to point fingers and say it would be your fault or their's, doesn't really matter. The point is that these kind's of situations can happen and you end up having to fill the tank role as best you can like the team player you are, which could result in you building one damage item to snowball your lane, and then building tank items for later on (the result being a 1-4-1 build like your friend advised).
Black Cleaver and Sunfire Cape are worth highlighting because they can be considered pseudo-tank items. Though they give tanky stats, they also provide some source of direct damage. Sunfire has it's AOE DOT (don't build Sunfire if you're jungling and built Cinderhulk btw, they dont stack). Black Cleaver provides stacking armor shred that the other AD champs on your team can benefit from without having to build it themselves (This procs on Wukong's ult, and stacks with his Q armor pen which is what makes it a strong item for him) So building Hydra-> BC-> rest tank items is perfectly okay if you're ahead and your team doesn't have a dedicated tank since it both provides some tankiness and benefits the rest of your team.
Hope this helps.
or 
. My best friend keeps insisting that the way to build them is only with a single damage item and the rest as defense, but that works against me in the end because I deal barely enough damage to make a difference, so I get relegated to nothing more than a meat shield rather than an active team member. Is there a way to build them other than this build, where I can equally have defense but also be able to deal enough damage to make a difference in team fights? Thank you in advance.