My website is just brief introduction about my activity, and where you can find what services provided, afterwards you contact me to design a website or other web services for you. Despite of this, frequently, I still recieve very short enquires as:
"hello, I need website", "hi, can you create ecommerce website for me" or "Pls. help. I need a better web page of my company".

These type of emails is not strange a bit, in your request email, you should specify as more details as possible, so that to recieve instant quotation. I thought about to put more fields in my contact form, but this might scare potential customers, that's why the form is simple and work for you.
But in your message body you should specify major aspects as:

1. What is your website domain name?
2. Do you have hosting?
3. What kind of website you need, any examples of your competitor websites you like.
4. Design preference - color scheme, layout, structure
5. What pages to be done? Page names, if ecommerce please specify categories, any extra functionality.
6. If your website to be database driven, please specify functions you need to be there.
7. Anything else you want to add.

So, another word, as rich your email is as easier for me to determine timescale and volume of work.