Starting to design web page layout from the scratch for a first time and want to know what's the best practice to set web page and all components on it measurements.
The page will have horizontal header with a navigation bar in it and a three columns beneath it.
That's what I've come up with so far:

* fixed hight in pixels for header part with horizontally aligned nav links
* fixed hight and width in pixels for web components
* components resides in a three columns (div elements) that has min-width set

Do I miss something or it's a good way to go?

PS I'm perfectly aware of Bootstrap etc, but cannot use any framework in this project, only pure html/css