would appreciate any opinions regarding around 20 floor joists which are running off level around 3 inches going across the joists from one end of the loft to the other theres a 70mm run and difference in height of nearly 3 inches.they run off in both directions across and in length.more so across from one joist to the next and so on. have had a few opinions from various joiners which they all have different ways and methods of levelling these joists.some would go onto the sides of the existing 6x2 inch joists with new timber and others would go in the opposite direction on the top of the joists and across them with new timber.thought cutting all the angles with new wood on top of the joists following in their direction would be the best process of levelling but not many joiners seem keen on that way as apparently theres a lot of angled cuts involved and some joists are slightly bevelled. need it levelled in order to lay chipboard flooring to use as storage space but would like it levelled correctly if it maybe gets converted in the future.any knowledgeble opinions would be truly appreciated. thanks