Preheat oven to 160 C / Gas 3. Grease and line a Swiss roll tin with baking paper.
Warm syrup, treacle, butter and sugar in a pan over very low heat.
Sift plain flour, ginger, baking powder, bicarbonate of soda and salt into a large bowl. Make a well in dry ingredients and pour in syrup mixture; stir in egg and milk until well combined, adding more milk if necessary to form a dough.
Transfer dough into prepared tin, pressing it down into a flat, smooth rectangle. Bake for 15 to 20 minutes in preheated oven or until gingerbread has hardened on top.
Use a template to cut out roof and walls as required, then allow pieces to cool completely on tray. Enjoy the scraps!