When do you think you are ready for creating your own application? You have to be good enough with coding but obviously that is not enough. The applications which you are creating for your targeted users, be it commercially or just for fun sake, need not be professional coders but are mere end users.The users want the developers to build applications that meet their needs and also help with it the easiest way . You need’nt be an artist for creating the best interfaces but should be able to deliver what the users want the easiest way.
GTK and Qt ,the same toolkits behind GNOME and KDE, are the best graphical toolkits fit for this job. Providing the same functionality they have their own advantages and disadvantages.
Check this How to add GUI for your applications ?