This is the spec we were set for the posts and poles challenge (what eventually became "The Fencelator"). The HTML and CSS restrictions were in place so we would focus on the PHP, but were allowed to add more front end once the PHP was complete:

PHP Posts and Railings Challenge

Overview:

Create a PHP application that can calculate the amount of posts and railings required to build a fence of a certain length or that will calculate the length of a fence when you provide the amount of posts and railings.

Requirements:

Specification: