Root Write Permission Cons

I have an application that 'publishes' html files using ASP. Based on
a hierarchical tree in the database, the ASP also creates folders to
replicate that hierarchy. For SEO purposes, I would like to keep my
directory structure as shallow as possible, such as having the home
page in the root directory. However, I am of the impression that there
are security issues to providing write permissions to the root
directory, let alone the sub-directories to which pages other than the
homepage will be written.

Thus, I am rather naive, and would appreciate answers to the following
questions:
1. What are the security risks?
2. Can I dynamically apply and remove write permissions from ASP
3. Is there a solution leading to the desired effect, without inherent
security risks? The site is on shared hosting, and URL rewriting is
not permitted.
4. What important issues am I failing to ask about?

Many thanks for your advice,
Iain