HelloNow I will tell you how to earn about 600g/h just farming Hellfire ramparts.
To start off you will obviously need a level 80, I would suggest a paladin, warrior druid or warlock as they got some nice tanking builds ^^, As for the Paladin, Warrior Druid the tanking specc is obvious. For the warlock I would suggest
Talent Calculator - World of Warcraft
You will be picking up mobs in 3 different pulls including the bosses. As show in the picture below.

To run the whole instance won't take you more than 13 minutes, 15 min tops.
The Gold making process.
You will try to get a full group to boost, 20gold per person.
You will also grab all the trash items, including the cloth and boss loot, you can also sell items that drops to the people you're boosting.
The loot per run.
You will get an average of:
4xRunecloth stacks
55 Gold in trash and boss loot
2xNetherweave cloth stacks
4xppl 20g each
I won't include the blue BOE item drops.
The math.
I will not include selling items to people you're boosting or BoE blue item drop.
Runecloth: 9g per stack
Netherweave Cloth: 7g per stack
55g in trash and boss loot
9g*4= 36g
7g*2= 14g
55g in trash
20g*4= 80g
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Total: 185g each run.
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185g*4= 740g/hour
It was suggested to add a gold/hour without boosting people
9g*4= 36g
7g*2= 14g
55g in trash
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Total: 105g each run.
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105g*4= 420g/hour
Let's say you pull of 15 min each run, that will be a total of 740gold/hour.
But, if you manage to pull of 10min each run, that would be a total of 1110 gold/hour. (but hey that's just a suggestion)
Also, if you don't have people to boost you will manage to pull off about 420gold/hour if you do each run of 15 min ofc.
But, with 10 min each run you will make 630gold/hour.
Thank you!