We report a reproducible top down fabrication procedure for a single domain wall magnetoresistance H-shaped device. A bi-layer e-beam lift-off process is used and the e-beam exposure dose sensing technique and proximity effect correction are discussed, together with a method to reduce the alignment tolerance to below 20 nanometer. The domain wall width is constrained down to 37nm and room temperature domain wall magnetoresistance ratio of 0.3% was detected. The dependence of switching magnetic field to domain width will be discussed, as well as the maximum domain width which can retain its magnetisation aligned along the long axis at zero field which is found to be 210nm in our experiment.