My biggest pet peeve (among many) concerning Tarot is when a so-called "expert" (i.e. anyone who has written a book no matter how good or bad it might be) makes ridiculous claims as to their way is the only way.
Bunk.
If you want to create your own spreads, create away. However, if you want your spread to have a decent shelf-life (i.e. it will be just as meaningful a year from now as it was on the day you created it), I urge you to follow some simple rules:
1. Less is More - You know that 32 card spread you're thinking about? As they say in those mafia movies... fuhgedaboudit! The more cards you add to a spread, the less significance individual cards will have. Overcomplicating a spread makes it confusing and impossible to read consistently
2. Be Consistent - Regardless of what your spread ends up looking like, it needs to be logical enough to be dealt and read consistently time after time. Create your own standards and apply them to every spread you use. For example, whenever I have a card in a spread which represents the querent, cards that appear to the right of that card indicate right-brain activity or influences (emotional, artistic, creative, following your heart) and cards that appear to the left indicate left-brain activity or influences (logical, rational, practical, following your head). When you follow this kind of consistent layout, you don't have to think about your spread in order to interpret it. From a basic glance you will intuitively understand it.
3. Be Logical - The layout should serve to remind you of the meaning of the positions. Again, look above at my right-brain/left-brain example. Another example, when I do a tree of life spread, the cards end up looking like a rough diagram of the human body. This way the interpretations can be associated with body parts that help me remember their meaning (example: right hip for drive - a right brain activity and left hip for direction - a left brain activity). I also highly recommend balancing your spreads... make sure there is a yin for every yang.
4. Be Specific - Don't try to make one spread which can answer any kind of question. You will never succeed. Think about the things you need to know to answer a certain type of question and name your positions for those specific items. Example: for a spread about making a choice between two or more things, you might want to know (a) what are the advantages of each option, (b) what are the disadvantages, (c) what do I see about each, (d) what don't I see, and (e) what can I expect. Depending on how many choices you are comparing, you have just defined how many cards the spread needs to contain.
By following these 4 simple rules, you will find that your spreads are meaningful and powerful. When you share them with others, they will convey a strong meaning as well.