- What portion of what you buy will you need?

- What is the cost of evaluating the integration?

- What is the cost of integration?

- Will buying increase or decrease long term maintenance costs?

- Will building it put you in a business position you don't want to be in?

You should think twice before building something that is big enough to serve as the basis for an entire other business. Such ideas are often proposed by bright and optimistic people that will have a lot to contribute to your team. If their idea is compelling, you may wish to change your business plan; but do not invest in a solution bigger than your own business without conscious thought.

After considering these questions, you should perhaps prepare two draft project plans, one for building and one for buying. This will force you to consider the integration costs. You should also consider the long term maintenance costs of both solutions. To estimate the integration costs, you will have to do a thorough evaluation of the software before you buy it. If you can't evaluate it, you will assume an unreasonable risk in buying it and you should decide against buying that particular product. If there are several buy decisions under consideration, some energy will have to be spent evaluating each.