Dear Chitra,
Apart from Article of memorandum, Cover Note (Application on letter head for Registration) you need to submit following documents to RDLC:
Form Number 1: information of Principle Employer
Form Number 1 Annexure: Information of Contractors to be engaged
Authorization letter (If you are dealing with RDLC officials other wise they will not entertain you)
Remember not to include any contractor who engages less then 20 workers.
If your company is engaging Civil contractors also get them covered under The Building & Other Construction Workers' Welfare Cess Act, 1996 and do deposit the cess.
Regards
Ajay Morolia