When we started designing our future home, we felt the advantages of custom plans outweighed the disadvantages.
We wanted a house plan that would fit our family lifestyle.
We poured through thousands of stock home plans, without any success.
That does not mean purchasing stock house plans is a bad option.
Each situation is different and in your case it might be the right choice.
Only you will be able to make that decision.
Advantages to stock plans:

• Cost will be considerable lower.
  A Custom plan by an Architect can cost several thousands of dollars.
  You can purchase a full set of stock plans for around $1000.
  
• Once purchased, stock plans are readily available.
  Our custom plans took over a month to design and that was with us being very diligent in providing the home designer detailed information.
  
• If you are nervous about not being able to see a finished product, before starting, stock plans might be the way to go.
  If you purchase stock plans, you can ask the architect if the floor plan you like, has been built before.
  You can also visit forums such as the homebuilding forum on gardenweb.
  You might find someone who is building the same house plan that you are considering.
  

Disadvantages to stock Plans:

• Stock plans are designed with the masses in mind and not the individual.
  In most neighborhoods today, that there is only about three to five house designs used.
  Sometimes, the outside elevation is changed but the inside is the same.
  
• Usually, only minor modifications can be made cheaply.
  Modifications can become very expensive.
  You can expect to pay $50 - $100 for minor modifications.
  If you have dozens of modifications, it might be cheaper to use a home designer.
  
• If your or a family member is handicapped, it might be difficult to find a stock plan that will work for your situation.
  
• You will want to make sure the company that you purchase house plans from, screens the home designers.
  Do not be afraid to ask for references and proof of their credentials.
  
• House Plans purchased via the internet might not meet local codes.
  If you are purchasing house plans online, does the company have a return policy, if the house plans do not meet local codes?

Before purchasing stock or custom house plans, spend some time studying your lifestyle.
Just because every new house you see, has a two story living room, does not mean it will be right for you.
Your family might need the extra bedroom.
By studying your lifestyle, you will be better equipped in designing a house or purchasing a stock plan that fit's your individual needs.