Here's all I have so far. Basically I wanna make this so that I can try my hands at being the DM when what we're doing right now is done (or if it ever does get done).

The basic idea is that the group finds themselves in an underground society that has had clockwork and steam for hundreds of years. The main thing is the war between two of the dominant churches the church of Vapora goddess of Steam and Clockla goddess of Clockwork. They both believe their goddess is the rightful bride of Monomon the god of trains. But all the fighting is giving power to the god of scrap (who needs a name). So anyone wanna try to help me actually craft this world? If so PM or reply and we can work on it.

2592525
Hm. So you'll need a base race, like the Deep Dwarves, correct? That would be a great race to have the Churches be. Also, have the other folks in the Undercommon attack from time to time
Aka the Drow, other Dwarves, and the Mind-Flayers. Don't forget the Mind Flayers.
And the Undercommon is basicly the giant network of caves underneath the surface. They can go very deep down in which you'd find the Deep Dwarves. And the Drow CREATE driders out of Drows who are a 'shame' to the name Drow. So yeah. that's my advice, and remember to have magic looked down upon, considering it's a techno place, not a magic one. So people might not like magic since they haven't truly SEEN it in a long time.

2592525 Very interesting setting and campaign but I would place the godesses a bit different. Steam is the combination of water and fire so I would rather place the fight between the two godesses of that - on the foreground it is a fight about who gets credit for the power of steam, in truth it is a fight about who gets worshipped for it and thus gains power from the worshippers' spiritual energy. Meanwhile the god of machines (which includes trains) fights against the god of decay (which includes rust). Magic could even be an integral part of their kingdom, but only in the form of rune magic - they see magic as just another natural resource but someone using magic directly instead of binding it into metal is a deeply unsettling concept for them. It is like comparing a combustion engine with a dragon's breath.

If you want to add a bit more depth to the setting I would make the god of corrosion in fact be a nature deity - the only use for metal he sees is as trace nutrients for plants, and the very thought of refining metals to use them as anorganic building material is incomprehensibly alien to him. As such his work of corrosion is not so much an act of malice (though revenge may play a role as soon as his followers start getting killed) but a reaction motivated by fear. His followers would work well as antagonists - first saboteurs, then assassins and a full-blown invasion. I imagine them like the Golgari from Ravnica.
While the god of decay and rebirth (as is his full name, all but forgotten by the populace of the Clockwork Kingom) is alignment wise chaotic neutral, he may have a good share of both chaotic good and chaotic evil followers.

Likewise the god of machines would be lawful neutral, though in his case it is more about obeying the laws of physics to produce solidly engineered machines - he abhors shoddy work. And he does not care for what these machines are used, only that they are built, and built well, so he could have his good share of lawful good and lawful evil followers.
What would work very well as their signature weapons would be clockwork crossbows - both heavy albarestes that use complex gear systems to even load them and a bolt from which goes straight through your shield, your armor and the guy behind you, and rapid-fire repeating crossbows that need to be wound back up when switching magazines. Of both weapons there would also be low-tech versions, but they would be inferior in piercing power and rate of fire respectively. And of course there would also be pistol versions of both. The repeating crossbows could even play a merry tune while they are fired. Maybe even different tunes for different gangs.
Another weapon that could be mounted on vehicles and steam-mechas would be water throwers and flame throwers - the former can also throw boiling water (or with the right cooling rune enchantments near freezing water) while the latter use very unrefined oil (if it is not ignited it is very slippery and can be ignited at a moment's notice and if it is ignited it sticks to victims and surfaces like napalm - they may have very well reinvented the legendary Greek Fire). Then there are of course also flour-based flamethrowers - you only need pressurized air and a torch. They would not stick to surfaces but are cheaper to reload. Then there also spring-loaded catapults - they again require a complex gear system to load but are very powerful for their size (Leonardo Da Vinci designed a few) throw a sack of flour and simultanuously fire some flaming arrows and you will ignite the resulting dust cloud.

Da Vinci style sickle chariots would also work well, especially for a purist faction that are against the use of steam as they see it as an aberration. According to them only the labor of the faithful (or at least animals) is worthy of the god of machines and any worship of the godesses of water and fire is heresy.
Maybe also clockwork golems that need to be rewound regularly. They would also make a good special unit for the clockwork purists - they are only ones that commune so closely with their god that they caught a glimpse at the principles for using rune magic to create a machine mind.

All things considered this could work very well if you make five deities and place them in the Chinese elemental pentagram - Air, Fire, Water, Wood, and Metal. This way the god or air can also join in the fight for worship for the steam technology. I imagine the god of air as an all-encompassing trickster god, all-seeing, all-hearing, but with a temper and mind as whimsy and spontanous as a sudden breeze - that is, it appears whimsy because we do not see the currents and calculations behind it. He could be playing the godesses of water and fire against each other, thus adding both their energy to tornado and tempest, and then, when both are weakened, swoop in and claim the worship for steam for himself.

2593899
First off sorry it took me a week I got distracted. Secondly I think I'll keep that in mind. I'll write both and see which my group thinks will be better. I plan on doing both eventually but this sounds like fun.