Much like any kind of construction work, there's apt to be a fair amount of mess and clutter left over after the work has been finished. Check with your flat pack assembly company to ensure that they will tidy all the mess up after they're finished. If they're prepared to both tidy up and dispose of all of the boxes and waste materials, that will be a huge bonus, so you shouldn't be afraid to ask. It is important that the room where the assembly took place is left in the condition that it was before they turned up, meaning they should clear up any sawdust, fixtures, offcuts or packaging.