Due to the possible variations of MDF’s properties, some part’s edges and grooves may need attention to allow them to join correctly. I.e. the bottom strip of the walls that slot into the pavement section groove and the pavement groove itself. Check each piece by joining them together (see the ‘Assembly’ page).
Using a file or sandpaper clean up the edges/grooves. Try not to over do this and check how each piece fits. It will be preferable to have to press the wall into the pavement groove, so it should not be filed until it is too loose.
Inside the wall sections is a groove for the floor piece(s). This to should be cleaned up and checked to see if the floor piece fits ok.