If you're looking for more capacity you'll want a bigger dehydrator. Once you start pricing them out you can find that these can cost hundreds of dollars.
Below is an example of a relatively simple design for a deyhdrator with 30 sq ft of capacity. Initial testing showed this design works, though testing is still in process.
There are enough pictures that a relatively handy person could build this with some typical hand tools. It also gives some ideas about materials and construction techniques that may be of general use even if you go with your own design.
Cutting the plywood
Here is a simple inexpensive way to get straight cuts in plywood using a straight edge (about $20) and a couple of clamps and a circular saw. If buying plywood at larger lumber centers where you know the dimensions, they will also do some number of free cuts.
The plywood used was 3/4" cabinet grade pine plywood. Cost is about $30 for a 4'x8' sheet.
Removing burrs from J-strip
One of the parts for the dehyrdator used to hold the racks on each side is called J-strip. It is normally used as an edge protector for sheetrock and is available at larger hardware stores near the sheetrock supplies.
I cut it to length with a chop saw which leaves a burr. This can be removed with a file or, if you have one, a belt sander using coarse (100 grit) paper. The J-strip can also be cut with sheet metal shears, which cost under $10 at most retail/hardware stores.
Installing J-strip (rack holders)
Here is a picture of the inside of one of the sides. The J-strip is fastened to the plywood using 1/2" auto-perferating phillips truss screws. Using a drill driver, these will screw right through the J-strip without having to pre-drill holes first. A section of J-strip was used as a guide along one edge and the bottom to keep the pieces lined up. The J-strip was butted up against the piece above and below it. This gives about a 1.25" spacing between racks.
Partially built showing inside of dehydrator
Here is a picture of the partially assembled dehydrator. The sides with the J-strip can be seen and a couple racks were added to show how the racks slide in/out. The empty section in the middle is used to hold a ceramic disk heater, which is the heat supply for the dehydrator,
The center sections are held in place with sheetrock corner bead and the same 1/2" truss screws that hold on the J-strip. The plywood can be nailed or screwed together. You're essentially just building a wooden box that holds the racks and heater.
Pictures of finished dehydrator
Below are a couple pictures of the front of the dehydrator. There are two doors hinged from the top that have knobs in the middle to pull them open. Each door has a boxer fan to draw air past the racks. Four 1" holes were drilled through the doors under the fans.
The power for the fans comes through a dimmer switch so that the fan speed can be controlled. The dimmer switch can be seen at the top of the dehydrator over the opening for the ceramic-disk heater.
On the lower section of each door is a latch bolt to hold the door shut. The picture on the left shows the ceramic disk heater used. It is slid into the opening in the picture on the right.