Hello,

I would like to convey my sincere condolences first. It is very difficult for you to evade the charges of Section 304 a of Indian Penal Code since the threshold required for applicability of this section are death of the person, accused caused the following death and the death caused was the result of any rash/negligent act done by the accused. It does not require mens rea like culpable homicide read with section 301.

For you to raise there was no contract will not help you as this section does not go into the discussion of the contract between the employer and the contractor. It can only be useful if it was under the Employees' Compensation Act. 

In your situation, you've done neglient act by omitting to provide safety gears to the workers. But you can contest the charges by saying there is no direct nexus between the death of the worker and the negligent act or omission by saying the worker was himself negligent and it had nothing to do with the omission of providing safety gears. Because remote nexus is not enough to invoke the applicability of the section 304 a of the Indian Penal Code. You can also contest the charges by saying you have rationally taken due care. In addition to this, you can also say that contractor was supposed to provide safety gears as he/she has been continuously involved in such repairing and changing of roof, there was no clear indication from the contractor that you should have provided safety gears for this work. 

It will be better for you to go seek the help from a good criminal lawyer infurtherance to filed FIR. Hope this response helps you. Thank you.