I need a plugin that checks compatibility

Im making a hobby site that basically without giving lots away..

You choose an item from a list, It then goes into a personal list (like a wish list)
You then choose another item, But if that item is not compatible with the first item it will still add to the list but a warning message will show “Item A and Item B are not compatible”

Each item is a size, which also ideally needs to be deducted for your allowed size.. So if you had a 100gb hard drive and added a program which was 7gb it would then say you have 93gb left of space.

Sorry I dont want to give too much of what im doing away 🙂

I can do PHP, But ive never done anything like this before, So If someone could at least point in the direction of a Plugin or something and then I can build from there or something.

Thanks