Assuming you have fulfilled all that was required of you under the contract for the building purchase, and assuming the contract meets all the requirements to be considered legally valid, you have two major options if the seller refuses to close: suing for specific performance, and suing for monetary damages.
Understanding Your Options
A contract for a building purchase is just like any other contract; it is a legally enforceable promise. If the other party won't live up to his promise, then the court is going to allow you to take action. There are two main actions that you can take in this case, depending on the resolution you are hoping for.
You can sue for "specific performance." This is an equitable remedy wherein you ask the court to actually make the seller close, go through with the sale and sell you the property. Specific performance is appropriate and likely to be granted if money really can't compensate you for the failure of the contract to go through. If the land if unique, for example, and all land is generally considered to be unique, then the court may order specific performance and require the seller to sell to you since money wouldn't allow you to just go and get a similar lot.
Another option is to sue for monetary damages. Instead of suing for specific performance to make the seller actually sell the property to you, in this case you sue for the actual dollar amount of any financial losses you suffered because of the seller's delayed performance or failure to perform at all. In other words, if the seller eventually goes to closing but two months late, you can sue for the extra 2 months of rent you had to pay on your current property, plus the difference in the market value of the property between the time of the contract and the day when the seller refused the closing if the property value has increased.
Whenever there is a potential breach of contract - especially when you have a contract to buy a building and large sums of money are at stake - you need to consult with a lawyer for help if you hope to have the best possible resolution of the situation.