Dewmz,
Hey man, I can see the how it looks to create your own dummy; But if your serious about Wing Tsun (or WC, whatever) it is better to find a good dummy and shop around online, or find someone to make a wooden one for you.
There are many things that can be practiced on a dummy, and other systems (Such as Hung-Gar) have their own specific type of dummies, that do different things. However in WT, the dummy isn't just to train our techniques, it is to train EVERYTHING. From our stance and positioning of body and limbs. Old Jong's were actually placed in the ground, having a spear like tip at the bottom that you buried. You want this resistance, because the dummy doesn't lie. If you attack the dummy too hard and without the proper positioning, it will throw you back, but if you attack a pvc dummy, there is a greater chance that you will succeed when in reality it is not teaching you the correct things. The dummy is self-correcting. I mean if you screw up the dummy will not give up and if you are clever enough it will teach you how to be soft, and where you can be hard.
I made my own dummy out of plywood, and I had a helluva time trying to get it to sit still. It didn't really help me at all, and when I moved, I left it there because in all actuality, it didn't help me in the slightest.
The reason to practice on a dummy is when you don't have a training partner, if you have one, and you haven't already learned biu-tze, I would say that you have time to wait on the dummy. Take your time with your art. It isn't a race to see how fast you learn the techniques. The principles and theories are if not more, just as important as the actual techniques. Because I don't care how technically proficient you are, if you don't understand the concepts and theories, you will never be successfull in wing tsun.
Footwork is one of the most neglected things in WT. If you can't keep your feet, do you honestly think your techniques will ever succeed? The answer is no.
I hope I've givin you some things to think about and again, no I wouldn't even bother with a PVC dummy. It may work for some people, and yes you can make it work, but you aren't using the right tool for the right job. You can do better for yourself, and when it comes to WT, I would expect someone with passion about it to do what is right.
All the best in your training!
Jeff