Most national forest campgrounds do not have tent pads. Please give me the name of the campground or click on the "National Forests & Campgrounds" tab to the left and find the campground on our website. We'll indicate on our website whether there are tent pads or not. If there are tent pads, to answer your question, you'll need to contact the applicable ranger district office for the tent pad measurements - that could be a challenge
If there is a tent pad and the tent dimensions exceed the latter, there again the Forest Service will have to tell you whether placing the "over-sized" tent on the pad is OK. I expect it would be OK, but . . .
Even if there isn't a tent pad, the tent size could be a problem fitting between trees or even on or at the end of the campsite parking apron - most NF parking aprons are 10' to 15' wide. If the campground sites are reserveable and you want to make a reservation, recreation.gov won't have a clue about your question.
Having said all this, I am confident there is a campsite that will accommodate your friend's tent configuration. You'll just need to work with the Forest Service a bit, or, of course, take your chances. The ranger district office is identified on our website. Will your friend be bringing his recliner? Sorry, couldn't resist