This worked out OK for me... I budgeted building a house with $50 sheathing and $7 2x4s... then the bank bungled my paperwork and delayed the start by 2 months. I watched in horror as sheathing went to like $90 and 2x4s as high as $9... then the prices came down a bit. My loan was then approved, so we waited a little longer to buy lumber. ended up getting nice 5-ply STR-1 sheathing for $19/sheet and will be under massively on my overall lumber budget.
Now, if only garage doors didn't currently have a 4 month lead time.