how can I build a free but professional website?

you can't unless you find a free domain host....... and if you want professional I would suggejest you learn: HTML, CSS, and javascript.

If you want a forum on your site you should learn PHP and MySQL

You can build a free professional website with Microsoft Office Live Small Business - http://tinyurl.com/olsbfree . Currently, MS is offering a free domain name (i.e. yoursite.com) for the first year. It also has a free online web design tool that allows you to create web pages without coding. It provides 500mb of storage and has no ads.

no there is no option for making free professional website. some websites provide u but that r the trial version for 15-30 days only.

What are you trying to do with your website? If you are looking to sell stuff, you should open a free store on a site like http://www.whyabe.com/

If you are looking to just create a personal website, you should check with your internet provider (whoever you pay for internet service) and see what kind of hosting space they give you. You could then download free software to help you create the site on your own and upload to your hosting place.

"Free" and "Professional" are two terms that NEVER go together!

OR you are an amateur, never to be taken seriously on the web, (Free sites are reserved to kids, blogs, self-ego trips and so on),

OR you are a professional, you PAY for your domain and your server, and you design your site using proper coders and techniques...