Can someone suggest a peripheral system involving 16 inputs?

I hav just entered final year of my B.Tech in E&C engineering n 2day wz my first class in final yr project . I am quit sure with d fact that i hav 2 make a project involving , Controling som device using Schineder Zelio PLC with 6 i/ps and 4 o/ps . It means if we use simple digital logic at o/p , we can control upto 16 devices by a single PLC module . Bt i m nt sure abt wt hard ware to control ??? earlier i thought , i could automate a multistoried car-parking building bt my groupmates said that it would b a below standard idea nt matching the expectations of our clg . so can any one out ther help me out by suggesting a pheriphral system involvinng a max 16 i/ps . I am absolutely sure that i would b comfertable wid the programing of the PLC