I am building a riser for the second row of seating, i.e. 92" sofa, and need some tips on carpeting the monster. Actually, how do you handle the corners. I have seen some corners that were professionally done but cannot seem to figure out what was cut or tucked or folded. Any tips or points in the right direction would be greatly appreciated. Your help will probably save our landfills from several yards of carpet. Thanks in advance.