If you need more space for your hobby or home business, there's an alternative to knocking down walls and adding on: install a backyard room. You can buy a stand-alone structure that really is an extension of your home, with well-sealed walls, double-pane windows and an interior that looks like your living room.

Do-it-yourself kits come pre-cut or in panelized sections (pre-cut kits are often less expensive). Make sure the manufacturer guarantees that any parts that arrive damaged will be replaced immediately. And before you assemble the room on your property, be sure you like the design; after it's built, you can't return it.

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Manufacturers leave it up to you to hire an electrician to wire your structure. If your power needs are minimal, you can probably connect a new circuit to your home's circuit-breaker box, run a wire to the room and add some wall outlets. But if you require more power, you may need a new panel box or even an upgrade to your home's electrical system, which will run a few thousand dollars.

Unless otherwise noted, the companies cited below make structures for delivery across the U.S. Keep in mind that prices are for the kits only; site preparation and installation cost extra. Most kits are do-it-yourself, except those that say installation is included (you may be able to hire someone to assemble the structure for a few hundred dollars). Each company offers more than one model.

• Cedarshed (www.gazebos-and-garden-sheds.com). A panelized kit for an 8-by-12-foot "clubhouse" costs about $3,000, including delivery. (You may be able to order at a Lowe's home-improvement store.) Delivery fees can add an extra $500, depending on your distance from the manufacturer, located in British Columbia.

• GDM/MetroShed (www.metroshed.com). A panelized kit for a 10-by-10-foot structure costs about $7,500. Delivery fees can add as much as $550 to the bill.

• Modern Cabana (www.moderncabana.com). A panelized kit for a 10-by-10-foot shed costs about $12,500. Delivery fees add up to $1,000.

• Modern-Shed (www.modern-shed.com). A panelized kit for a 10-by-12-foot studio costs $11,980, plus delivery fees of between $400 and $2,400.

• The Shed Shop (www.shedshop.com). Serves customers in the San Francisco area. A basic kit for a 10-by-10-foot backyard room costs about $5,400, including installation.

• Summerwood Products (www.summerwood.com). A panelized kit for an 8-by-12-foot standard structure costs $4,440, including delivery.

• Lindal Cedar Homes (www.lindal.com/sunrooms/gallery). The Michael Graves Pavilion line of panelized structures includes three models that are built by Lindal Cedar Homes and sold through Target stores. The Sherwood is 13-by-13 feet and costs about $10,000, with an additional $3,000 in delivery and installation costs.

Before you assemble the room on your property, be sure you like the design; after it's built, you can't return it.