Use a hall closet or linen closet for your washer and dryer and cover them up with bi fold doors.
Doors to cover washer and dryer.
Interesting use of doors to cover the washer and dryer with a counter on top maybe in the hallway in the upstairs.
If everything looks right and the doors open and close correctly go ahead and screw your top into the sides of your cabinet attaching all three main pieces together.
If you have a stacked washer and dryer set design your cabinet to cover both of them with one large door that can be opened to reveal the front of both.
Sliding door install a small sliding door across the entrance to your stacked washer and dryer.
Once each door is mounted to each side you can put your 3 sided box back over your washer dryer for another fitting for any final adjustments.
For a side by side front loading washer and dryer set two separate doors work best.
By old world kitchens custom cabinets.
Sliding doors that retract into the wall or slide behind the wall usually require professional.
Just another option kivaallgood.