To make easy channels for roundwire for a dollhouse, try a grout saw. A grout rake or grout saw is a simple inexpensive hand tool used to clean out grout between ceramic wall or floor tiles. The grout saw makes cutting shallow channels for dolls house round wires as simple as erasing a line. No need to risk cutting yourself with a utility knife, no need for a dremel tool in tight spaces.
To use the grout saw, which works wonderfully on MDF (medium density fiberboard), mark where you want your wire channel to run, and rub the grout saw back and forth along the line. It's that easy. The carbide blades make short work of MDF and the width of the channel is constant, making it easy to tape over or fill after the wire is installed for your dollhouse electrical system. The angled handle on most grout saws makes it easy to work the tool into corners and if you do a lot of dollhouse wiring, the blades are easily replaced.
These tools are available from building supply stores, hardware and tile suppliers, usually for under $5. You can also use them to create grooves in MDF for paving lines or to draw out flagstone shapes.
For more information on round wiring a dollhouse, see start wiring a dollhouse which explains the differences between round and tape wiring systems as well as the advantages of each.
For information on purchasing a transformer, see How to Choose a Dollhouse Transformer.