108687 simple php banner ad rotator

i need a simple php based banner/text ad rotator with timer. I want to be able to rotate three ads each in separate php files. I want to code in an include file which picks between the three php ad files and then rotates them every 30 seconds. so i will call the include file.. ad #3 shows..30 seconds go by..then ad#2 is shown...30 seconds...then ad#1. And then this cycle repeats. Must be expandable to 10 ads/pages as well as time must be adjustable. Please comment code. Need rights to code too. Yes ive seen a ton of these. please make for me.