We are planning to convert an old stone garage into a small self-contained studio. It is a very old building but essentially just a rectangle in shape with a slate tiled roof. It has electricity and is not listed. We know how we want the space designed - it's a very simple layout - but would need plumbing etc. It has two windows which we will replace. I don't think we need an architect but will need drawings for planning. Also advice on insulation etc. What kind of company/person do I approach for this? Would appreciate any advice or tips!