One way to chew up a large amount like that is to apply the closing cost money to the PMI or MIP up front fee, or a VA the funding fee. Those fees are 'allowable', but you cannot only partially apply funds to those fees. It an all or nothing matter. If you have $8000 in closing costs covered by the seller and your actual closing cost is $6000 you have $2000 left. Depending on the price of the house that is probably not going to be enough to cover the fee so it will be rolled into the loan. If you apply it to the fee first, you will be short on normal closing costs and will have to make up the difference by bringing more to the table.
Either way it plays you are not entitled to the overage. The builder could offer $100,000 in closing costs, but if those costs are only $6000 that is all you get.
The question I have is how did you have $8000 in closing costs? I sell a bunch of new construction 14 last year, it is about 25%-33% of my business, and closing costs have rarely exceded $4000. We had one this year that was $7000 and that was due to some outrageous lender fees.
As far as the fence goes it depends on how the contract was written. If it says that the builder will include a fence, 'up to 200' of 6' cedar stockade privacy fence with 2x4 cross bracing, set with capped steel posts, and will include 2 gates, one on each side of the house.' then he has fulfilled the contratual obligation and I can't imagine why you would think that you would get money back. IF, on the other hand, the contract was written with an allowance for various items, like '$2700 allowance for up to 200' of fencing' then you can reallocate left over fencing funds to other areas of the house. For this reason we do not write contracts with a fencing allowance. We price it with the home. Light package, appliance package, trim package, and others all have a specific dollar amount allocated to them. We had one girl who was allocated $900 for the light package and she only spent $300 on the whole house by shopping hard for 2 months. She was able to allocate the $600 to other upgrades in the house.
So the easy answer is probably not. But there are ways to negotiate with the builder to accomodate for this $500 shortfall in a legal way. Feel free to call if you wantto go over these.
By the way, I am a lender and not a licensed realtor. Please consult your realtor before making a decision. Thanks!
Ultimately, if no gift card or "credits" addendum was done prior to closing, and nothing else is in writing to cover what part of the $8000 went where, you may be "out" the $500. If your Realtor is persistent enough, and the Builder hopes to sell another home in your community, he/she may give-in and provide something. Client and Realtor feedback can make or break a Builder's presence in a community, (I know from experience on both sides).
Best of luck!
It appears by your statement that the builder promised to give a credit of $8000 towards closing costs. If your closing costs were actually less than $8000, then the builder does not have to give you the difference. In fact he probably can't. If he does, then he could be in violation of the Real Estate Settlement Procedures Act (RESPA). He gets to keep the difference.