Look at it another way, say you needed a conservatory on your house and it was going to cost £20K, a friend said he'll build it for you if you get the drawings done, which will cost £200, why would you turn him down ? You are getting your property improved at virtually no cost to you and added value for when you sell the property.
So it turns out your mate wanted you to pay for the drawings, buy all the materials and build it yourself.