If you need, I can help you build your website.

I'd like to participate in developing your website, and I'll try, as much/far as possible, to help make it a wonder.

I can make some contributions to the building of your website.

I'd appreciate it very much if you could/would get me involved in designing your website and I will make every effort to work for it. 

这几句语气很不相同，最后一句近乎哭求。

对你的句子，只改一处：少用 I want to...