Is the ROM how everything looks?

So I have a Samsung Galaxy S2 and its the only Android phone I have ever had, and when I first got it I liked the phone and I heard it was a really good phone at the time but I really hated the look of the software. Because of this I tried multiple different launchers like Apex, Nova, GO and so many others but I couldn't get the status bar, notification menu, system settings panel and all the other system stuff to change. I then had one of my good friends root and flash a new ROM onto my phone (SlimBean 4.1.2) and the staus bar, notification menu, system settings panel.... all changed to a much better look, much cleaner and much more 'stock androidy' but I'v never really thought it looks that great. 

My question is, could I hyperthetically change how the status bar as well as all the other system features of the phone looks by changing the ROM? Is it the ROM's that manifacturers develop to make there phones look different from one another, TouchWiz to Sense for example?

How hard is it to make your own looking ROM if that is the case because I will be getting the HTC One but I want the software to look as 'fashionable' as the phone does, as clean and eligant as iOS 7? 

While a rom can potentially change how things look, thats not all it does.  A ROM stands for read only memory and is literally like the OS. When you flash a rom you are pretty much replacing the os with a different build of android. ROMS can have better performance, more features, and change the look. If all you want to do is change the look you can just install a different theme or skin. Building ROM is not easy at all and I know it requires knowing a good deal of java and other languages though im not sure which ones.


As far as your question on what manufacturers do they do develop specific roms for their phones which are forks of android. However touchwiz and sense aren't roms themselves, they are skins which are specific to samsung and htc roms. 

A good way to try it out is to do an Image Backup of your current phone state that you can refresh back to incase you decide you dont like using a custom ROM.  This will bring your phone back to the exact way it is now without any changes.

Then find a ROM you would like to try out and follow the instructions included along with it.  Usually any and all of this information can be found over at XDA Developers.  It is definetly the best place for this kind of help, no offense to TekSyndicate.

My personal preference is CyanogenMod 10.1 for custom roms.

Aww cmon guys, you know this man wants a more simple answer!

Okay, so, a ROM, simply, is your operating system for your phone. Like windows, linux, or mac. There is a "default" ROM, and that is from Google, and it's called AOSP (Android Open Source Project). I can get in depth on what different ROMs do, but all you need to know, is that the status and notification bars, and literally every image on your phone that makes up how it looks, CAN be changes if your ROM has something called "theme chooser".

I can go in to depth, but basically, look in the features list of a ROM for "theme chooser", or get a ROM based off of CM (CyanogenMod) because CM always has theme chooser, and nearly all ROMs based off of CM have it as well. Now, if a ROM says it's "Odexed", it basically means, it cannot be themed. 

Now, a theme you can download from the play store, much like a launcher. Some you pay for, some you do not. When you apply a theme however, it can change some, or all of how your phone looks. Most change the status bar, notification bar, nav bar, system icons, and some of the stock apps (like phone, messaging, and such).

That is the simple route. There are other ways where you, on your own, can change each individual part of how things like. So you'd select and image to replace your status bar with, and so on. This is what you'd want to do if you want to make your phone look the way you want EXACTLY. However, unless you're good with image editting, and plan to make the theme by yourself, I wouldn't really go that route. However, if you don't want a pre-made theme, and do want to do this, I could try and help you out and get you started, but we will have to get you more used to your phone to do that. 

Getting a ROM with theme chooser, downloading and applying a theme though, is much easier, and usually the themes look pretty good and you can find one you like. In fact, go to the play store now and search "CM themes" or "theme chooser themes" and check them out, see if you like any.