I bought the Lego Brand Store (set #40574) last month in the Lego store in Brighton, England.

I never like buildings when they don't have a roof, and it seemed odd that half the building had one floor, whereas the other half had 2 floors so I extended the top floor over all the ground floor.

PARTS LIST:
With thanks to ‪@RobbMajor‬ in the comments below, who put this parts list together for everything you need for this MOD:

PLATES
1x 8x16 Dark Bluish Gray Plate
4x 8x6 Dark Bluish Gray Plate
2x 1x1 Yellow Plate

BRICKS
2x 1x4 Tan Brick
4x 1x3 Tan Brick
2x 1x2 Tan Brick
12x 1x6 White Brick
2x 1x8 White Brick
6x 1x4 White Brick
8x 1x3 White Brick
4x 1x2 White Brick
2x 1x1 White Brick
6x 1x4 Yellow Brick
2x 1x1 Yellow Brick
10x Brick, Modified 1 x 1 with Stud on Side
8x Brick, Modified 1 x 4 with Studs on Side

TILES
8x 1x6 Tan Tile
4x 1x2 Tan Tile
26x 1x1 Tan Tile
4x 1x6 Yellow Tile
2x 1x6 Light Bluish Gray Tile
2x 1x1 Light Bluish Gray Tile
4x 2x2 Light Bluish Gray Tile
4x 2x4 Light Bluish Gray Tile
4x 1x2 Light Bluish Gray Tile

SLOPES
16x Slope 30 1 x 1 x 2/3