You will have to be registered under the category of Consulting Engineer Services with Service Tax department being under the control of Customs, Central Excise authorities. You will have to find out first under which jurisdiction/range your business/professional address falls and then apply in Form ST-1 and in turn you will be issued certificate of registration in Form ST-2. Certain documents like, photostat copies of PAN, proof of address, constitution of business etc., are to be enclosed to ST-1. No fee is required to be paid. Application shall be made within 30 days from commencement of your services. The jurisdictional Supdt. of CE shall, after verification of application to his satisfaction, grant ST-2 within 7 days of submissin of application. If regn. is not granted within the said time period, it shall be deemed to have been granted.