Beat butter, syrup and brown sugar in a medium bowl with an electric mixer until creamy and paler in colour. Add combined sifted flour, spices and gum; stir until mixture just comes together. Knead dough gently on a surface dusted with gluten-free plain flour until smooth. Wrap dough in plastic wrap; refrigerate for 30 minutes or until firm.
Preheat oven to 180°C/350°F. Grease two oven trays; line with baking paper.
To make side walls: roll one-third of the dough on a surface dusted with gluten-free flour until 3mm (⅛-inch) thick. Using wall template, cut out 16 squares; place 3cm (1¼ inches) apart on trays.
Bake for 10 minutes or until lightly golden. Slide paper and walls from trays onto a wire rack to cool. Cool and reline trays (see notes).
To make front and back walls: repeat with rolling half the remaining dough. Using end wall template, cut out 16 walls; place on trays. Bake as directed in step 5.
To make roof: repeat rolling remaining dough. Using roof template, cut out 16 rectangles; place on trays. Bake as directed in step 5.
Make royal icing. Sift icing sugar through a fine sieve into a bowl. Lightly beat egg white in a small bowl with electric mixer until mixture is just broken up – do not whip into peaks. Beat in the icing sugar, a tablespoon at a time, to reach the required consistency. When icing reaches the right consistency, stir in juice. Cover surface directly with plastic wrap until ready to use.
Fill piping bag fitted with a fine piping tube (no. 2). Pipe icing onto shapes, attaching side walls with front and back walls to make a house (hold in place for a few minutes to stabilise, if necessary). Pipe along the top edge with a little icing; position roof (hold in position, if necessary). Repeat with remaining pieces to make a total of 8 houses. Stand for 30 minutes or until icing is set.
Using picture as a guide decorate houses with royal icing. Stand for 30 minutes or until set. Just before serving, dust with sifted icing sugar.