Since this bookcase is inexpensively built from MDF, the hardwood trim is key to making it look more expensive and well-put-together.
The trim hides the gaps between the cases, and along the wall, ceiling and base.
I used mullion between the cases (and even made some of my own) .
The key is to use solid wood (plain or with a decorative edge) to cover the edges of the MDF, and frame the bookcases against the wall and ceiling.
I used a 1x2 (3/4”x1-1/2”) along the left wall, and a piece of stock ripped to 3/4”x3/4” along the right wall where there was a tighter fit.
I used quarter round between the wall and the door surround. On one side the gap was too deep for quarter round so I used shoe molding which is like a quarter round molding that’s been elongated .
I used boards ripped to 4-1/2” wide to cover the bookcase bases. My baseboards were then nailed to these boards.
Finally, I nailed two long 1x2 boards along the top of the bookcase. My crown molding will be nailed to this to complete the look!
All the trim is done, the cases have been primed 2 times. The only things I have left to do is build the shelves, install the crown molding and build and install the cabinet doors to the bottom half.