Nothing special about a harvest ale - just substitute into a regular recipe, with 7xfresh hops compared to regular dry hops, to allow for the water content.
But obsess about freshness - I know commercial brewers with a lot of experience of green hop beers who aim to have them in the wort within 4 hours of picking, and refuse to touch hops more than 12 hours old. So they start the boil, and then go to the hop farm to pick up the hops. If you can't use them the same day, get them drying.
One problem is that you don't know the alpha content of the new season hops, so bittering becomes a bit of a lottery - and for normal people with limited amounts, it's a bit of a waste to bitter with green hops when their USP is the volatile aroma compounds that are lost in hop drying or boiling wort. So concentrate on dry hopping and whirlpooling to really get the benefit of them, but if you've got plenty then it certainly won't hurt to use them as late-boil additions.
