Wall cabinets and base cabinets are constructed differently, but there is no reason a wall cabinet can't be used as a base. Many people choose to do this as extra storage in a hallway, a window seat in a child's room, or in a bedroom in lieu of a chest of drawers. This is a relatively simple process and only requires a few tools.
Step 1 - Make Your Markings
Line the cabinets along the wall where you eventually want them installed. Use the pencil to create a template by tracing out the outline. Move the cabinets out of the way after you've made the outline. Find the studs in the wall and mark them.
Step 2 - Create the Base
Use the 2 by 4 to start a base. Lay these flat on the ground so they are the same width as the cabinets front edge. Set these back 1/4 inch. Use another 2 by 4 along the back flush against the wall. This will create a tailored look and make it easier to install the cabinets. use the wood screws to secure these to the floor. Be sure they are flush all the way down.
Step 3 - Place the Cabinets
Set the cabinets up on the bases you just created. Use the pencil to mark the interior of the cabinet where it lines up with the stud marking. You will need to create a pilot hole through the cabinet so you can secure it to the stud. Use 2 screws along both the top and bottom edges. Use the same process to secure the cabinet to the base by drilling through the 2 by 4s.
Step 4 - Finishing with Veneer
Measure the front of the cabinet where the 2 by 4s are exposed. Cut veneer to this size. Attach the veneer with the construction adhesve. This can be finished off with the finishing nails. The base of the cabinet should now match the cabinet itself.
Wait at least 24 hours for the adhesive to dry before using the cabinet.
Finish the top of the cabinet to your liking. For a window seat, find cushions that fit the top of the cabinet. Otherwise you can use veneer in this area as well since wall cabinets are not usually finished at the top.