To start farming gold from 0 is kinda hard, so I hope theulas give you all good advice about that
But once you getlegendary weapon to sell on TP, it becomes easier.
You can just craft legendary weapons and get profit from that.
For example, I would recomend crafting Twilight/Sunrise because those are 2 popular weapons.
Crafting each of them cost like 850-950g raw materials + dawn/dusk. Then you just need to farm SW chest for obsidian shard (or use your karma, bandid crests etc.), ascalon tears and medals of honor from pvp playing.
So in the end you will pay around 900g for raw materials + 750g for dawn and you will get Sunrise. You spent around 1650g for it, and you can easily sell it for 2800-3000g on TP. -15% fees = 2380-2550g. That means you can get almost 1000g profit from crafting legendary Sunrise.
It takes 2-3 days to get materials from TP (if you wanna buy for low price). Ascalon tears will take you one day of farming, badge of honor with playing pvp ... no idea how much time because I had tons of them while levling in pvp.
So probbably obsidian shards will take most of your time.
Also when crafting legendary, you wil need Mystic clovers. Price to get them isn't fixed and it depends purely on your luck, so it can cost 100g more or less.
In the end you will get gold profit from crafting legendary for sure.
edit: Forgot to mention 100% map exploration xD
When you complete 100% map exploration you will get 2 items that are used in legendary crafting. So with one character 100% map completion you can craft 2 legendaries.
Takes some time, but in the end you can profit massive amounts of gold.