Opinions on NLTK

Hi, I've been studying NLP for a little bit now and would like to do a project where I create a one sentence summary of a paragraph. I want to start off by analyzing sentence structure and creating a parse tree for each sentence. From the more experienced people, I'm wondering what are your thoughts on NLTK? Are there reason's why I would write my own parser? I don't have a lot of experience with NLP, so I'm wondering if NLTK is something I should always look at using when possible or if I would be better off learning the material myself and implementing my own tools.

Thanks in advance.