As an architect, you consider many things before starting any design. Here are some things to consider before you start.

1. What is the problem I am trying to solve? 
   

2. What direction do you face? 

   North, south, east and west have benefits and disadvantages, though north (in the southern hemisphere) is generally best for most purposes.
   

3. Is the budget critical, or is the solution more important?

   No fence-sitting.
   

4. How does your floor level relate to the ground?

   You are well raised off the ground (at least 0.5 meters), or will you need to retain some soil.
   

5. Do you need to improve the connection between existing spaces? 

   Inside and out, or up and down?
   

6. Is there a particular item (e.g. furniture) you are trying to accommodate?
   

7. Where will you need new walls, or would drop-down blinds work?
   

8. How will any new roof be attached to an existing top?
   

9. What sort of lighting/atmosphere are you trying to achieve?
   

10. How will you address natural light and ventilation?

If you can answer these, you should be well on your way to designing your little extension.