Gather these parts

Glue the side walls together as shown.  make sure the bottoms line up and that the slots near the lower back on each are also lined up.

Glue the sides slotted into the back plate as shown

You’ll need to do this step and the next in quick succession so you may wish to read ahead.

Glue the back and sides down to the base and quickly move to the next step before it sets.

Glue the roof onto the pegs on top of the sides.  This will help straighten the walls into the correct position. 

Glue the tops of the side rails in place

Glue the bench strut into the slot along the back wall.

Glue the detail plate in place on the back wall so that it touches the side walls and the floor

Glue the bench into the slot in the back wall

Glue the clear acrylic plate under the roof to finish the model. 

You may wish to add this after painting.