When you purchase a VR Land, there is a chance you will receive it already with a building on it, so you won't have to build it yourself.
Of course, if you do get a building and for whatever reason, you decide to demolish it to build something new, you are fully able to do this.
Whilst it will cost you some resources to demolish the building, you will also get some resources back. How much you get back will depend on the type of building you have. In some cases, demolition will be beneficial and other times you will have to pay for it.