Best way to make a template?

[Discord]

Hi, i've been working on making a new site and before i started using php i always had to recode the template page into ever page on the site (very tiresome and nightmare as far as storage and maintence is concered). Now i have coded a single php file that open other files and displays there contents. My question is this... what do you guys think is the best strategy for making a template based site in php, as far as ease of maintence is conerned?

Here is the simple fopen i've been using on my site.

			<?php
				$displaypage = $_GET['PG'];
				if ($displaypage=='') {
				$displaypage = "home.html";
				}
				$filename = "includes/$displaypage";
				$whattoread = @fopen($filename, "r") or die ("Couldn't open file");
				$file_contents = fread($whattoread, filesize($filename));
				$msg = "$file_contents";
				fclose($whattoread);
				echo "$msg";

		?>

[marque]

I like to use the address bar a lot when it comes to makeing a tempate driven page

firstly I create an index.php page

before anything else I create this

<?php
if(!isset($page))
   $page = "welcome";
else
   $page = "design/".$page.".php";
if(!file_exists($page)
   $page = "design/error.php";
?>

then i put my pretty design in

and right in the middle of the page where i want my content to go i put:

include($page);

then i create a directory called design where i can keep all my content pages in.

eg design/welcome.php, design/about.php

I can apply a different style sheets to each page if I want and each page is self contained so I always know what i am working on.

When I want to put a link in I call ?page=about or ?page=info, ect