Count down timer

I am looking to build an LED timer with buzzer. The timer will have digits for 99hrs 99min 60sec . Not that I will ever use 99 hours but as long as I will be building this, might as well have maximum capacity available. Trying to make it as small as feasable and still be portable. I know there are a lot of timers I can buy in the stores, but, they all have one VERY annoying feature to me. That is they sound off 10 & 5 minutes before your set time. I want a timer that sounds off ONLY after the set time as elapsed. I was wondering if anyone new where I might find a schematic and parts list for such a timer. Thank You