If you know PHP and MySql its great. If you are working with Joomla I can suggest an excellent component Called Sobi2 which had a very good interface for the user as well as the administrator. Excellent templates and customizable CSS. You could work on a good structure like the Categories and the Sub-categories without any limitation in the depth. The most Herculean task is to create the structure of the categories. Go through different web-directories and you could get good idea how to design your category structure. Some of the user interface that is provided by Sobi2 is that you add unlimited custom fields, good access control so that I can control who can do posting and editing or deleting an entry.

As far as a visitor is concerned, he can search using key words you can enable some fields to search category like the user can select websites from a particular country and entry a key word for the search. Other things that a user need is something different from a Search Engine like Google or Yahoo. You should provide some interface which can be more impressive, like preview of the website, rather than visiting the website, if the visitor can get a brief Idea of the what that particular website is about and how the website look like. If you provide a preview or a screen shot of that particular website, the user may remember the website if he had already visited and can decide if he needs to go there again or not. He may not remember the URL of the website, but if he sees the preview he may remember that he tired that website or not.

Web directories should be organized well and when a user select a particular category he should see only the websites from that particular category. For Example create a category called Health, then some sub-category Hospitals, Pharmacy, Laboratories, Doctors, Nurses. Its like refining the search. If the visitor is looking for Hospitals In India, he can just go to Health and from there he can select hospitals in and the country too. He gets what he really wants to. The most important thing that you should be very careful is the selection of websites. You should visit each and every website before posting it or approving it, that?s very important. This is one of the distinction what we can make from a machine search and searching on a human edited web directory.

Other things that you should provide for a web-directory is like add some links of recently added websites, and you can make some provisions for the user to rate a website and even write some review which will be useful for the users visiting later.

More over its like a page for every entry and a brief information about the website and provide some vital information like the contact details, phone number, email address. It should be fine and do not forget to add a link to that website, very important. How long and how far can you go building a web-directory? I cannot say that, as the World wide Web is Unlimited with Millions of Site. For best of your interest and to provide the best to the visitor, you need to select a category for your web directory. So that you can concentrate on what you want to provide, rather than making 100's of categories and sub categories and just 10-15 websites in each category. I would suggest is like select a main category and start building your web-directory under that and expand your sub-category. You should start adding websites concentrating on the main category. For example if you See the EmailMe Web-directory, the main theme is India. In this web-directory, you can find websites from India with all the categories under that. In this way you can start building and if you allow user participation you can get building your web-directory with great pace. You need to keep updating the links and if you can provide a provision to report dead links, that would be great.

This piece of information is from work that I have done on building EmailMe Web directory

A software programmer from Carnegie, working on PHP, Mysql and doing some research on Google, Pagerank, SERPs and SEO currently. You can find my blogs at http://me.googling.in and my Web Directory Project at http://www.emailme.in