A common new business mistake is to assume that you need an office or a storefront immediately. If your house is zoned to allow a small business, then use the space you are already paying for.
Many service businesses -- a cleaning service, plumbing service or roofing operation -- don't need an office at all [source: Nolo.com]. Your "office" can be the front seat of your van with a cell phone. All of your work is done at the client's site, anyway.
If you're convinced that you will need to rent space for your new business, then it should be part of your business plan. Make a detailed list of the location's requirements. How much space do you need? Do you want high foot traffic? Will you need parking? Do you need visibility, or is it OK to be tucked away in a suburban office park? What are your zoning requirements?
Then you need to do research into the rental market. What is the average monthly rent on a place that meets your criteria? Consider consulting with a commercial real estate agent who really knows the local market. Once you have a price in mind, lock it into your budget and don't be tempted to splurge on the perfect location.
Also remember to budget for improvements or alterations that will need to be made to your location. If you want to open a restaurant in an old shoe store, plan for significant costs to install a professional kitchen and bathrooms that are up to code.
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