This is a legal Q&A site, not a business advice site. You need to do some research and general background reading in starting a business. NOLO Publishing has some good DIY startup guide, but they're legal, and you need need business information.
I'll address the most obvious legal aspects of your query. I assume you mean "Craigslist," not "Craglist." You should assume that Craigslist has registered copyrights on their webpages, and even if they haven't registered their pages, you can't infringe on Craigslist's copyright on their site. That means that the "look and feel" of your website site can't be "substantially similar" to the look and feel and feel and their site's pages.
You also can't infringe on Craigslist's trademark/servicemark rights by branding your site something confusingly similar to theirs, such as "Craglist," which even you have already confused.
Avvo doesn't pay us for these responses, and I'm not your lawyer just because I answer this question or respond to any follow-up comments. If you want to hire me, please contact me. Otherwise, please don't expect a further response. We need an actual written agreement to form an attorney-client relationship. I'm only licensed in CA and you shouldn't rely on this answer, since each state has different laws, each situation is fact specific, and it's impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue.
As Ms. Koslyn indicated, if you are going to start an internet business, it would help you to read some books on the subject (see link below). Once you have a bit more knowledge under your belt, you will want to engage an intellectual property attorney in your area who has experience helping people to start internet businesses.
Good luck to you!
Any answer or other information posted above is general in nature and is not intended, nor should it be construed, as legal advice. This posting does not create an attorney-client relationship between you and the posting attorney, and you are urged to engage a qualified attorney who is licensed to practice in the relevant jurisdiction.
There are 3 legal things to do right away:
1. get a lawyer
2. get a lawyer experienced in internet law.
3. get a lawyer experienced in Internet law, business law and intellectual property law.
Don't try to cut corners on the legal aspects of this. The Internet is much like the Wild West and you need a sheriff to help steer you straight so your business does not wash down the grand rapids of legal white water.
You received some great general advice, but really you need to see an attorney specializing in Internet startups to outfit you properly for the rough waters ahead in doing an Internet startup. There are millions of such startups and most go bust either from lack of funds, lack of originality, lack of customer or lack of legal advice. Be sure you have all four of those areas covered BEFORE you launch.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.