If you have the experience, and the tools, get the plans and build it yourself.
You can also get the plans and have someone else build it for you.
Those first two are recommended, as you have the opportunity to customize it.
I also recommend that you build mock-ups from cardboard and duct tape to get the proper dimensions down that you will need. Not all magicians, and not all assistants are built the same in terms of size. So you are going to get the details down before putting all your money and effort into building an illusion that is not going to work for you.
When you purchase a ready-made illusion, you are hoping that it is going to work out for you, and also fit your style aside from the paint which you can always change yourself.