Solutions for wood rot in an old tongue and groove screened in porch

[Sandy Uhlmann]

I have a rental that was built in the 1920's.  It has a tongue and groove screened in porch that is in good condition except for some significant wood rot at the junction where the porch joins the landing to the steps.  My contractor says it is due to water/snow sitting there.  (drainage issue)  He says that it is near impossible to replace the boards in a tongue and grove porch and he proposes that we cut out the old rotted wood and try to find some sort of grate or old metal floor vent to put in its place so water can drain through the floor.  the size of the grate/vent needed is something like 12X 32 as it is right below the screen door.  We have looked at the grates that are used for sump pump driveway drains as a possibility but we are having trouble finding something this size to fit.  Does anyone have any other solutions to this problem?  Any advise would be appreciated.