Works contract

If the services if pure repair services of Building it shall get covered under Construction Services Clause (iii).

If your services involves, material on which you've paid VAT, then Works Contract Services. 

In both of these you can opt for composition scheme.

IMP : There's a Service under the Head Management, Maintainence & Repair Services which department uses as the tool to charge service tax at full rate. Hence, beware categorizing for Repair Services.