Start with Orb of Blight and whatever stats you need, can be a null talisman for mana and/or a wraith band. Then do Treads for bonus attack speed (you could also do Bearings if they have some crazy aoe slow which slows your entire team or Greaves if enemies have a silence that u need to dispel).
If you're getting some gold from kills, turn Orb of Blight into Desolator to stack -armor but if the situation is dire, upgrade that Orb of Blight into Orb of Corrosion (btw. u could also do it in a normal game as a support, I mean Orb of Corrosion without getting reported, you'll be auto-attacking poison-touched enemies who try to get away so the bonus slow and some agility is useful)
But let's say you have Treads and Deso, now it's time to do Aghanim Scepter - to also send an attack each time you chain Shadow Weave onto enemies, it refreshes poison touch on them and Deso applies minurs armor with these E attacks, so your physical skills can deal more damage. You can also go to jungle and farm pretty fast with Aghanim, which is important if the game goes for longer and u want to finish your build.
Then, I'd build even a later Mage Slayer - Shadow Weave attacks from Aghanim will apply the spell damage debuff onto them, which helps you win teamfights and makes a big difference, it's a good item because of how easily Dazzle can apply it after Aghanim and they will also suffer from additional physical damage DoT, which work with your armor reduction.
So we have Treads, Desolator, Aghanim, Mage Slayer. Now, I'd say it feels that you lack attack speed for a serious r-clicker build. I'd do just green Yasha for some bonus movement speed too, and Dragon Lance for bonus range. Then, you can go two routes:
Dragon Pike ofc lets u send 5 fast attacks which can be easily clicked by sending your projection into the middle of the fight, but there's also something useful with Force Staff - when you start your ulti clone, turn back and send it behind at you at first,, it won't matter for range but your body will be stunned facing that backward direction, if someone attacks you, you can Force Staff your original Dazzle back to try and save it... or u can start ulti while facing direction of some hill where they wont be able to jump if you push yourself through the cliff, or a more aggressive version, you can Force Staff your original body forward to have more range when they are escaping - something similar to pushing yourself as a burrowed Nyx :D
The second option (pretty good actually) is Hydra's Breath, because when we Poison Touch multiple people, our multi-attack from it will allow to extend the poison on all of them. I'd for sure do it if enemies have illusions. Plus you will apply an additional dot onto the enemy with Shadow Weave attacks, which scales into late game because it's a %max hp damage. Dazzle is one of the better user of this item, as he has an invulnerable projection that doesn't need survival if he doesn't get found.
Ofc if someone is VERY keen on finding you during your ultimate, u can tell your team to help you and with this build, u can try to simply Shadow Grave yourself and kill him before it expires :D Yet if its very troublesome, u can try to do something like a normal Glimmer Cape to hide your original body or Eul to yeet him into the sky and try to get away, don't do Ghost Sceptre because it will be used by your Projection and it won't affect your tripping body xD
So now we have Treads, Desolator, Aghanim Scepter, Yasha, Mage Slayer, Hydra's Breath. It's 6 slots, wooops, so if u need detection, I guess get Aghanim Blessing. Now, I kinda like to upgrade Yasha into Yasha and Kaya... for attack speed and ms, but also for faster casting xD Because in late game, damage gonna be very high that you might not be able to cast your save in time, lol! This helps to activate it quickly and not get spam-pinged + tipped by your Sniper who just died to one enemy crit.
(Ahh I forgot, you can do that Yasha and Kaya even earlier if you have mana problems and if you indeed have troubles in clicking Shadow Grave in time)
It's propably the end game now, if you dont have to carry detection, I'd do Eye of Skadi as my last item to apply a slow and minus regeneration with each attack + each Shadow Weave chain will also apply it + these stats are good for an universal hero. But we already have slow with Poison Touch, so it's not as decisive, but it's nice to stack more slows and turn them into a snail faster. Ahhh and I quess since we have Yasha and Kaya for movement speed, u can play without Treads and get some another late game item for damage, like Daedelus Buttertfly or Rapier, or if u need to carry wards/gem and can only be 5-slotted, sell Treads and get that end-game item instead of boots, that's what this Yasha and Kaya is also for, to be able to play without boots. But if u do better boots than treads, like Bearings, u can skip that Yasha item, as you are already fast enough and ofc dont sell your Bearings :D
You can ofc check a lot of different items, all r-click items will work - Butterfly for attack speed, Daedelus for damage, idk maybe Mjolnir or Bloodthorn. I never tested getting Assault Cuirass to stack -armor even further haha, u can check it out, aura will radiate from your projection in the middle of the fight. But if you feel like you still lack attack speed, u can get Bloodthorn instead of one of these items I listed, whatever you like.
Your final items might be:
Yasha and Kaya, Desolator, Mage Slayer, Hydra's Breath and one/two of these: Eye of Skadi, Daedelus, Assault Cuirass, Butterfly, Bloodthorn, MKB.
(I guess if enemy mages have BKBs and they mostly fight on it, your Mage Slayer won't affect them and u could sell it for more auto-attack damage, but if they don't do such blasphemous things like a BKB, u can keep it and keep debuffing them even into the late game.)
The end :D
