I laughed when I read this, "why all beginners need to use patterns". Believe me, we have all been where you are at one time or another. I agree with most to make the small ones, one size and then cut the squares to that size. You will lose your points. but only you will know it wasn't on purpose. When I make up a pattern, I first make a sample out of scrap "to make sure it works. I am challenged in "the making your own pattern area" also.
I do my pattern on graphed mylar, then add the 1/4 in to each piece for the final pattern size. I'm sure there is an easier way but this works for me. If you don't have 1/4 in foot on your machine consider getting one, it is a big help to keep your seams accurate. It is my favorite tool and has made a huge difference in my seams. Don't get discouraged, it'll look fine, it'll have personality. Show us when you're done.