Painting work for building

I am doing painting works of building. Getting amount from customers Rs 20 lakhs pa. Of this I purchase Rs9lakhs painting material(Bill in the name of Customer)i.e.I just purchase material on behalf of customer. On balance Rs11lakhs I get profit of about 2lakhs only. Max transaction are thru bank. Any service tax liability for me? Can I show my profit as commission and brokerage and avoid service tax. If 11 Lakhs is shown as turnover service tax comes and I wont get any work.