We do not need to create custom CSS grid, framework or whatever you like to call it. There are already so many professional frameworks are availabe. We dont need to waste time on those which is already available in marketing with remove all those bugs which may occur in our custom css framework.
How ever there are advantages and disadvantages to use third party css framework. Before use it, think that is it required to use it for small task or not. Suppose your site is simple and you can create your website in responsive with few links of code, then i suggest dont use css framework, because generally css framworks have large files. In this case, instead of get benefit from css framework, it may overload on your page even if it is simple. So before use it you just think yourself. I am not telling that css framework is bad. It is already good to use it, but it depends on situation and your website design layout. In market there are so many css framework like Twitter Bootstrap Grid module, Zurb Fundation, 960.gs, The 1140px Grid, and more.
I suggest to create you own css framework and use it if possible in your small scale website design. You website will load very very fast if your css will be in small size. You can measure it when you will use both css framework and your custom css. Finally, its your own choise what you want to use.