REGARDING INPUT

If you are providing warehousing services than for agriculture produces as prescribed in GST Act is exempt from tax, so you are not required to charge GST in your bill.
but if you are providing warehousing services to other than agriculture produces, which is not exempt from tax, than you are required to charge GST in your bill, collect and pay it to government.

If you are registered under composition scheme, if eligible, than you can't collect tax from recipient. You are required to pay tax at prescribed composition rate.