You must know the different organelles if you are going to model them. Vitally, you must understand their shape. The colors usually given to the different cell components in text books are used for contrast and usually bear no resemblance to reality, so in that instance you can be creative. But you must develop the correct shapes in order to model them.
It is also important to know how the various cell structures relate to one another. For example, the endoplasmic reticulum (ER) is always located close to the nucleus because if processes the proteins that are used in DNA replication. You must understand this fact as you are creating your model.
Know the differences between plant and animal cells. Most importantly, plant cells have an exterior cell wall made of cellulose, contain very large vacuoles (a membrane-bound collection of water and enzymes), and possess chloroplasts (the portions of the plant cell that convert sunlight into usable energy)