Before you order your Factory Five Roadster you’ll want to spend some time on the forums and learn what your options are. They are http://www.ffcars.com and http://www.thefactoryfiveforum.com. Also check out http://www.clubcobra.com. It’s not Factory Five specific but it’s good to see how other Cobras do things.
Sign up on the forums and start reading. Find builds you like and talk to the owner about them. They’re usually happy to tell you all about their cars. As you become more familiar with the options you’ll form specific questions. Try using the search feature on the forum before posting your questions. It’s likely someone has asked the question already and sometimes forum members will get testy at the repeat.
Start a build plan document and list your goals for your build and the options you want. At first you can make it pretty general but as you learn more you can make it more and more specific. I like to break the document into sections that follow the major build areas. Those are chassis, suspension, brakes, electrical, fuel, engine, cooling, drivetrain, interior, body, and paint. Detail each area as much as possible. This will help you down the road as the Factory Five build manual can be a little general and certainly won't cover any upgrades you're planning on.
Once you have your plan you need to compare what you want to the options Factory Five offers. If your list closely approximates the Complete Kit then that will be a good option for you. If you are deviating too much from a standard build the Complete kit can be a large waste and the Basic Kit is a better buy. It's important to note that in addition to convenience and potential cost savings the Complete Kit offers another advantage. If you don't have a lot of experience building cars the Complete Kit provides a solid baseline for your build. You'll have the benefit of possessing all the necessary parts that you might not otherwise be familiar with and from there you can upgrade. That is how I did it but now that I'm familiar with the he process I would start with a basic kit.
The last piece of advice is wait for a sale. Factory Five doesn't have them often but if you're patient you can save a lot of money on accessories.