Sagging porch repair costs and cause?

[Jack Lee]

Hi I'm looking into purchasing a property and was wondering how much it would cost to repair a sagging porch. This is in a historical district so I have to restore the porch to original standards. 

See below for a picture of the house front:

Any thoughts on how much this would take and what is causing the sag? 

[Nick C.]

Costs are different depending on your area, so I won't comment on that. When we see that sagging down here it's generally termites, the roof leaked and wood rotted, or a combination of both.