If it needs a new floor John, theres a possibility that whats below the floor may need replacing as well, plus the transom, unless you are going to do the floor yourself it could be very expesive ££££'s 
Has the engine got service history ?
Has the hull had major surgery ?
Are you using it as a speedboat of fishing boat ?
What safety equiptment comes with it...i.e life jackets, flares etc ?
Check the trailer bearings, hitch, tyres etc ?
Why is your mate selling it ?
Might seem a damning list, but if some of these things need doing, you could end up with a massive bill.....
The best bit of advice already given is to take someone with you who knows about boats.......Good Luck mate...
