The cost of your backyard design Walnut will depend on the materials, decors, plants, and labor needed to turn it into a reality. If you put pathways, you can use paving solutions like stone pavers or brick pavers. This usually costs around $3 to $15 per square foot. You can also add a patio to your Walnut backyard design. A patio can cost you around $800 to $4,000. If you want your backyard to be more functional, especially if you are hosting family events, you can place an outdoor kitchen to your design. An outdoor kitchen may cost between $2,000 and $10,000 depending on the appliances and materials that you will use. Some homeowners include a fire pit on their Walnut backyard design. A fire pit has many styles and usually costs around $80 up to $7,000 from portable to high-end custom. You can also add organic grass turf to your backyard to add some flash of green. It can cost you $200 to $500 to plant grass on your yard depending on the grass type.