Whether you require a banner advert or web site, the more information you can provide the better.

Here are some examples of what we need to make a web site:

Business Card (or same details and logo eg on letter heading)
Leaflet (or text about hotel / restaurant / tour services etc)
Pictures (the better the pictures, the better the end result)
Prices (eg room rates / meal rates etc)

The best guide is to ask yourself what you would say to someone you hope will become a customer or to look at what has been done by companies already with web sites such as those you can view from the guest sites page.