It's all about trading gold for stats. Every item has a different gold efficiency. That means it costs a different amount to get similar stats. Knowing what items are gold efficient means you will effectively multiply your gold.

Imagine you have 1000 gold. If you buy an item that is 80% gold efficient you have reduced your value to 800 gold. An item with a 120% gold value would increase your stats by 40% over the item with 80% efficiency. You could have 40% less farm than your lane opponent and still have an equal value because you traded your gold for stats more efficiently. Also, you could beat your opponent by 40% and have 196% of their gold value since you would have used your gold lead to secure the extra 16% stats (40% of 40).

Its important to note that these items in this build are gold efficient without their passives and actives. The value of passives and actives are largely subjective, and largely are determined by their relevance to any given champion. For example, Spellblade, found on trinity, iceborn, and lich bane may be useful to different champions, although its a similar active. Additionally, champions with long cooldowns likely will not benefit as much as champions with low cooldowns as they wont make use of the passive as often. If a champion isn't able to fully utilize a passive or active, then the value of the passive/active is reduced merely because its on that champion.

All of these items stats and passives/actives work with Ekko's kit. That is important because its icing on the already gold efficient cake.

Rod Ages (full stacks): +1,368 additional gold value

Berserkers Greaves: +315 additional gold value

Nashors Tooth: +1,198 additional gold value

Spirit Visage: +615 additional gold value

Hextech Gunblade: +715 additional gold value

Warmogs Armor: +150 additional gold value

Total additional gold value: 4,361

Early:
Play safe until you get a gank, level 6, or ROA. This build snowballs hard naturally from 15 minutes on. Patience is important early. CS, and try to deny farm. Whatever you do, just don't die, and always call MIA.

Mid:
Push in lane and look to roam. Once you have ROA and BG you will hit your first true power spike. Abuse it, and make sure to keep your CS up.

Late:
Use your stun to zone. Burst any enemy that's low with your execute. Peel with Q. Be a team player, and focus objectives. Ward. If you get an advantage, take as much as you can. Don't overextend or overstay.

CS>Towers>Kills

Ignoring the passive gold that everyone starts with, CS accounts for approximately 80% of the average player's in game gold. Towers and champions kills each account for approximately 10% each. Knowing this, maximize your gold advantage by getting as much CS for yourself while poking your lane opponent to minimize their CS. This sounds like a simple concept, but League of Legends is built in such a way that the player base generally idealizes kills. There are like 10 LoL voice overs for getting kills, but none that give praise for CSing or getting towers. Don't fall victim to prioritizing kills over CS, towers, or objectives and you will further maximize your gold.

Thanks for reading, and best of luck to all on the Field of Justice!