My client is requesting a general quotation about the design and development of their site. What I need is the specifications that I should evaluate the quotation on, such as if I need to host the domain, site responsiveness, multi-language, etc. How can I make a "general" quotation before knowing what will be on the site?
Your client expects specification document which is nothing more than a list of all features, man hours for each and your hourly price. This can be a usual word document with text only or excel sheet with table and additional calculations like risk or unpredictable events, etc. If you're writing it for the first time, then a normal work doc is OK. You may format it to look more professional if you like.
Now, design and web development are two totally different things.
Design - I would give client a rough price for the design + let him know how many changes he can have for that price (5 for example). Yes, limit number of changes or you may end up doing touches on a small image for 1 month. To know the price you need to calculate work hours you need for this project. There is also a situation when client is willing to pay all time spent on design, but those cases are rare, at least with me and my friends.
Coding - make a list of all features. Do not miss any and do not think that some feature is implied. The client will know that you are estimating the price for the listed features only. This will also be a type of agreement between you two. The list of features can be as simple as this:
Landing page (you may also add a description of it) 1a. Left menu 5 man hours 1b. Right menu 10 man hours 1c. something else
About screen 2a. Email feature 1 man hour
In the end you put TOTAL and count man hours.
As third part you may add hosting price and your monthly support or something.
If this is a "sure job", then make a list of features detailed ones. If this is only to see if the client will move forward, then list only high-level features letting the client know that you two will later make more detailed specs.
Ask if I missed anything.