Global Navigation Across Site

I am trying to set up a global navigation across my entire site (to be found in the header area). I do not wish to hardcode the links, but rather have them dynamically generated. Note that I use categories as navigational elements.

I currently have two “sub-blogs” installed upon my website. It is as follows:

– https://www.katskinner.com (the home page)
– https://www.katskinner.com/about (standard about page found in the main site)
– https://www.katskinner.com/contact (standard contact page found in main site)
– https://www.katskinner.com/writing/ (a sub-blog).
– https://www.katskinner.com/writing/category1/
– https://www.katskinner.com/writing/category1/posttitle
– https://www.katskinner.com/writing/category2/
– https://www.katskinner.com/writing/category2/posttitle
– https://www.katskinner.com/coding/ (a sub-blog).
– https://www.katskinner.com/coding/category1/
– https://www.katskinner.com/coding/category1/posttitle
– https://www.katskinner.com/coding/category2/
– https://www.katskinner.com/coding/category2/posttitle

I wish to display drop down menu’s for my header. So without scroll over the user will see:
– Home (katskinner.com)
– About
– Writing
– Coding
– Contact

If the user was to scroll over “writing”, they will see something like the following (and so forth for any sub-categories):
– Home
– About
– Writing
– category 1
– sub category 1
– sub category 2
– category 2
– category 3
– coding
– contact

How can I code this in wordpress?