Hi reno, welcome to BYC!
 
The hardware cloth is important so that no predators can reach in and grab a chick.  A coon can and will pull them through a dog crate or kennel fencing.  We use dog kennel panels for some of our runs, but we still put hardware cloth on the bottoms, and down about 12" underground.  
 
Your chicks will need a place to be able to get out of bad weather.  Grass is fine on the bottom, they will gobble it all up very quickly.  You might want to look at some of the A-frame tractor plans, you could do that with pallets, and be able to move them around on the grass.  The investment in hardware cloth is worth not having something eat your chickens.