Legendary equipment comes from having a high, maxed out smithing skill and not potions. I think you are referring to using Enchantment, Alchemy and Blacksmithing to create very powerful items.
1) Make Fortify Alchemy Gear
2) Wear Fortify Alchemy Gear
3) Make Potion of Fortify Enchanting (With Fortify Alchemy Gear)
4) Drink Fortify Enchantment potion.
5) Use increased enchanting skill to create better alchemy gloves than you could previously and repeat until you hit the cap. (29% I believe)
6) When you have hit the cap create fortify smithing, AND a potion of fortify enchanting.
7) Drink the fortify ENCHANTING potion.
8) Use this to make incredible Blacksmithing equipment.
9) Equip these items and drink Fortify Smithing potion
10) Upgrade your weapons and armour with new shiny stats.