Custom Atrtributes

Hi,

i want to add custom attributes to OpenCart. What i want to have, is attributes with a dropdown of pre defined values, like for example:

Items in Package:

• 1
• 2
• ....9

Where the one that adds the product can only select the options from the dropdown (and later i want to add an extended search, where the frontend user could select values from the dropdown for the search)

I have almost no experience with opencart development so far, but i am a long time php developer. What would be the best way to do this. Is this possible in form of developing an extension or do i have to patch opencart (i would be open to adding this to the official source)