You must follow the process of software development, in stages or phases as stated in the rules. In the development of a web portal can intervene several people who play many roles, but basically can not miss the information architect, information analysts, designers, computer scientists, among others. However, the development of a website there are several documents to be developed that record all phases, for example: Manual information architecture reflects the site's name, objectives, audience, or purpose, expectations and needs of the target audience. Lifting customer requirements, the techniques applied to selected users to assess the content will be published (tag names navigation routes to follow to find what content), non-functional prototypes (which They reflect the portal structure and organization of content). This is only the documentation leaves the information architect in the first phase. There is also the documentation of analysts, as user stories with each process to develop in the portal. And programmers codes that are stored in libraries and repositories.

You can read an article I published in my profile on the development of a web portal is in Spanish, but I think you can serve user-centered design: a case study of a library portal. I saved around have more literature on the subject, if you give me your contact I can send more e-mail. I hope you serve my explanation. Excuse my English.

As Liuris said it is quite important to follow practices in software development, taking note of every issues that involves it.  Also the scope of your project will lead you to narrow mission and objectives, but also how many people are in it. Software Management and Engineering is essential. If you are working in a team you maybe interested in how to manage from a team perspective and count what can not be apart of documentation in the process. Best regards

http://www.sei.cmu.edu/reports/00tr023.pdf

Hi

I recommend this project from the beginning is inclusive, meaning that your website is for all types of population. Also it is a business website.

I recommend using 9 areas of project management which allow you to optimal development. such as: (a) Management Project Integration; (B) Project Scope Management; (B) Project Time Management; (C) Project Cost Management; (D) Management of project quality; (F) Human Factor Management Project; (G) Project Communications Management; (H) Risk Management Project; (I) Achievement of Project Management.

For further information please consult the Methodological Guide PMBOK v5.0

You can start off with writing the content of the document first as headers i.e., Project Costing, Human Resource, Project Plan, etc.,. Once you are done with, you can fill out information which is required to finish the project.

Any type of project requires documentation as it keeps you focused on your objectives which are achievable ... I hope it answers your question