I'm sure there are many different factions (mostly modded ones) that allow you to take control of stations that have the same cores as the standard ships you know and love, but gameplay may be lacking as your mobility is compromised.
Capital ships can be played by just increasing your P level over time with infinite P mods to get to fly those giant 13000+ modded ships without using commands or whatever.
Also you can copy their designs by viewing them in diplomacy mode and dragging them into your ship menu, if you didn't already know. But make sure you have the required P and blocks in order to play as those designs.

There are also many different resources for improving ship building like some of the numerous building guides for the game. I personally recommend taking a look at many of them collectively, it's improbable that only one of them would be the holy grail for all things shipbuilding, otherwise practice makes perfect.

Okay thank you

also how do you go into diplomacy mode, sorry

Originally posted by FoxMage:

I really wanna play as some of the capital ships/stations of factions and was wondering if there was a mod that could do that, also I want to get better at building ships so does anyone know a way i can get better?

I recommend checking out some of these guides:

• A General Guide
  
• Strategic Ship Design
  
• Those Pesky Octagons
  
• Custom Faction Creation (a little bit out there)
  
• Other Guides!

A quick search on youtube for a reassembly lets play could also be a good way to learn more info on the strategy and basic flow of the game.

Originally posted by FoxMage:

also how do you go into diplomacy mode, sorry

No worries, should be tab, you can then hover over allied ships and press 3, allowing you to view, edit, or take their design. (Also it's actually called command mode, sorry if it caused any confusion)

I also recommend taking a look in at other controls in the pause menu in order to look at some other game functions and experiment a little with the keys of the game. May be hard to learn all the different functions right off the bat, but you'll learn them with time.

Thank you!! I figured out how to become one of the ships! thanks!

Originally posted by FoxMage:

Thank you!! I figured out how to become one of the ships! thanks!

No problem man