Dude I have Rank 7 on Jayce and about 200k Mastery points across 3 different accounts. The comments I'm seeing you leave, I really can't tell if you're blindly following the pros or just genuinely want to better yourself on Jayce.
Youmuu's is good, but that's because pro players know how to properly watch and utilize their mana. It isn't like "pros didn't build manamune, so I'm not going to" It's still an insanely amazing item that synergizes perfectly with him and I build it in 99% of all games I play.
These are the items I use, and I wont replace any of them:
....why? Because pros build those items nothing else can be viable? Don't get me wrong, pros are great and all. But other people have good opinions and champ builds too and it doesn't mean that I'm not good at Jayce either, I'm great as him. Try other builds, that's just a normal game mechanic that you need to learn if you want to get better.
Your build is okay but it lacks a lot of resistances so if you have a hard time in lane or overall you can die pretty quickly. Merc treads or a Sterak's go a looooong way.
Muramana is useless on him now unless you are new with him. Lords is bad on him due to BC's passive and Jayce Cannon R Auto Attack. Guardian Angel is ok, but Jayce isnt a bruiser, he made to sit back and poke enemies with Q+E, and is meant to destroy structures/wave clear.
I'm not going to check your ranking on Jayce but like even if it was pretty high, that statement is just flat out untrue. Muramana is not awful, Lords isn't a bad item on him (although usually I build mortal reminder) and Jayce is a bruiser? He's either all-in or all-poke, and playing him as a glass cannon ranged marksman is nothing compared to how he is meant to be played.