How to Build a DIY Custom Built-in Around Window

Add unique style and storage to your space with custom built-ins.

Creating custom built-ins is a great way to add a fun display space to any room. The task can seem overwhelming especially when building around a large window. But it is easier than you think! Learn how to build a DIY custom built-in and get more storage and design space.

Creating custom bookshelves is a great way to add a fun display space to any room.

When we built our new home we left the bonus room unfinished. I have been looking forward to finishing this living space. The focal point of this room will be the built-in bookcase and shelves, plus extra seating if needed. I wanted a space to display my decorative items and add plenty of storage.

Supplies Needed for a Custom Built-in Around Window

Most of these items can be picked up at Home Depot or a local hardware store.

4 - 2x4s
3 sheets of ¾" thick plywood
MDF molding
Shims
Brad nailer
Miter saw
Table saw or circular saw
Tape measure
Spackle
Sand paper
Caulk
Primer
Paint
Level

Shop all supplies here

Where to Use Built-in Shelving?

Family room
In the Home office or library
Living room
For entertainment centers
Dining room

Any space you can add built-ins is a win because your home will look more elegant and custom.

How to Build the Base Cabinets for DIY Custom Built-ins Around a Window

How to Build Custom Built in Bookshelves

Building the Base

The first step is to build a base on the floor. A good base will give the custom shelves extra strength and a good foundation. Using your 2x4s, attach them to the wall studs and anchor to the floor.

When building the base I wanted the bottom shelves to be larger than the upper shelves. The bottom cabinets measure 36" wide x 31" tall x 15" deep.

Since these walls are smooth adding a back panel for the built ins is unnecessary. If you have textured walls you can easily add back panels to your built-in cabinets. I added vertical shiplap to my mudroom lockers and it adds a lovely design element instead of using cabinet doors. Be mindful of your electrical outlet when determining backing and shelf location.

Next, rip down the ¾" sheets of plywood into 15" strips to be used as support for the sides, top of the cabinets, and bottom. Cut them down to size as needed.

I wanted the sides of the cabinets thicker than ¾" as it creates that custom shelving look and it is stronger. So I used ¾" plywood on the interior and exterior of the shelf side piece and then used strips of ¾" plywood as a spacer in the middle, between the two large pieces of plywood. There you have the bottom of the cabinet.

How to Add Shelves

Once your box is built you can add a shelf using shelf hooks in your custom cabinets. I am not doing adjustable shelving mainly because I didn't want the holes up and down the side.

The first step is to figure out where you want shelves. For the bottom shelf cabinets I am putting the shelf right in the middle to fit the storage baskets I found. Using baskets is a great way to add closed storage for built-in shelving. The next step is to apply the shelf hook to the back wall.

Molding adds a custom look to builtin cabinets

To install your hook, find your studs and apply wood glue to the back of your shelf hook. You will then place your shelf hook where you want it and use your nail gun to secure the shelf hook to the studs in the wall. The glue and nails combined create a very strong bond. I built a custom closet this same way. (View it here)

Add the shelf hook to the side panels as well, using the same method. Next, add your shelf and nail it down into the shelf hook.

TIP: Pull out your level and adjust your shelf hook block along the wall until it is level. You can use shims to get it 100% level. This will easily be covered up with molding and looks great.

Adding Molding to the Shelves

Once everything is built it is time to add molding for that custom built-in look. Rip down MDF to the exact thickness of the box and frame the whole thing up. The molding is a great addition for thickness and making it look high end.

Built-in Around Window

Here is the DIY custom built-in base all complete. Since there are custom windows in the middle we opted to build a custom window seat. I used 2x4s and then covered it up with vertical shiplap. The middle of the window seat bench is hollow for extra storage in the room.

How to Build the Upper Custom Shelves

Attach Spacers and Sides

First, attach the spacers to the side wall and then attach one of the cut side plywood boards to the spacers. Again, make sure that it is level and don't trust the surrounding walls.

Add Shelf Hooks to DIY Custom Built-Ins

Once the plywood side piece is up you can figure out shelf spacing. My bottom shelf is 15" tall and the other shelves are 13". I wanted the bottom shelf to be a little bit taller for bigger items.

TIP: Measure how tall your top shelf is and then decide shelving heights from there. This will help all the rest of your shelves to be evenly spaced.

Add the shelf hook to the back wall by placing wood glue on the back side and then nail it to the wall. Make sure it is level.

Install Spacers and Shelving

Once all of the shelf hooks are up, you will attach the opposite piece of plywood to the shelf hook.

Add the bottom spacer and nail it into the bottom bookshelf for added strength. Then add other spacers all the way up. Attach the exterior piece of plywood and secure to the spacers and other plywood board.

Next, add the shelf hook to the sides of your interior plywood boards and begin adding your shelves. Nail the shelves into the shelf hook on both sides and the back. This will give LOTS of strength to the custom bookshelves.

Finish Work for DIY Custom Built-In

Add a piece of plywood across the top as well. This will improve the strength and we will use it to attach the crown molding.

Finish everything off trimmed with molding because it makes a huge difference in looking custom.

Once everything is built go back and fill in the holes with spackle. Sand down all the rough spots and excess filler. Caulk all of the edges for a nice smooth finish and your DIY custom built-ins are ready for paint.

Paint DIY Custom Built-in Around Window

Tape off everything in the rest of the room that you don't want paint on, including flooring, your new window, and walls. Prime your shelving first since you are using raw wood. Sand it down after it has dried for about 4 hours.

Now you can spray. I painted everything with Cameo White by Behr. After I applied the first coat I used a brush to get the hard spots the sprayer couldn't reach. I then gave it one more coat of paint.

Cameo white by Behr is great for moldings

DIY Custom Built-in Around Window

Don't these beautiful custom built-ins make a statement for this entire room? The shelving adds a fun display area for decor items.

We chose to go with a dark wall color, Graphite Charcoal by Behr. The dark paint accent really helps to make the custom shelves stand out, along with the natural light coming in from the wall of windows.

Don't you just love that cozy window seat with beautiful throw pillows to soften the look? The baskets and the bench add closed storage for blankets, board games or anything else we might need in our bonus room.

You can see more detail on the bonus room here

These new custom floor-to-ceiling built-ins are not only a budget-friendly option, but they also add to the value of your home. Go the DIY route on your next custom build.

Try out this corner custom shelf here!

Happy Building!

Brooke