How do I get a Home seller build a fence prior to me purchasing?

Make it part of the offer.

But be aware they may throw up some cheapo crap fence just to abide by the letter of the contract and leave you stuck with a sub-standard eyesore that you are obligated to accept.

You simply make an offer that requires the seller to build a fence. Offers can include virtually anything. I'd caution against this because the seller will probably reject your offer or have the cheapest fence known to man built (unless you include all the specifications in your offer) and you will be obligated to purchase the house anyway. It's not that big of a deal to find someone to build a fence. Just look in the phone book. Any decent contractor will take care of all the permits, contact the electric company, check local regulations, etc.

Good Luck if you expect them to put in a fence expect to pay a higher price for the home.

Make your offer and make a fence part of the deal. The escrow willnot close unless all the terms of the deal have been met.

why would any seller do that? what if they don;t have the cash to get it done? 120 days is nothing.