Today was the day when I got bored of my Twitter background so I decided to change it.
The outcome can be seen by clicking the above image or here: @Garcya.
If you would like to create something like this you should know a few things:
Image size in px depends on what results you want to have. If you would like to have info / logo / text in the left side and nothing in the right the image size should be somewhere between 400-450 px width. You can toggle with the size for best view.
The image height should be around 860-900 px. My image is 860px height and it fits a resolution of 1920 x 1080 on Firefox without any toolbars.
After you’ve created your image you should go to http://twitter.com/account/profile_settings and change the background image, and after that change the design colors, especially the background that should be in the same color as your image background.
Hope this helped, but if you have questions you can ask here on follow me on twitter: @Garcya