Replacing our Car Port Roof

Leodogger

We have a car port that was probably built some 20-30 yrs ago with timber supports, fencing on the outer perimeter with a corrugated lean to sloped roof which when new was probably see through but is now filthy and difficult to get clean. We want to keep a see through roof as our front door is on the side of the carport. We have considered changing it for a polycarbonate one as they seem easier to maintain and keep clean as there is nowhere for the dirt to go whereas ours, it seems to get under the panels which are screwed together. We have attempted to get it cleaned once before but as I say it was impossible to get underneath the separate panels.

What I want to know is it better to replace the corrugated panels with flat polycarbonate ones and do they last a lifetime ?

The_Last_Username

is it better to replace the corrugated panels with flat polycarbonate

Well no, not necessarily; it depends upon your point of view.

You see, polycarbonate (either twin-wall or triple-wall)has - obviously - an air gap between the layers. From past experience, no matter how effectively you think you have sealed the open edge it will over time show evidence of condensation between these sheets.
Think of a windows' double-glazed unit that is not sealed for an idea of what will happen; warmer on one surface than the other = condensation forms.
This leads to discolouration which also cannot be cleaned/removed.
Also whilst polycarbonate may be easier to clean (being flat as opposed to ridged), it will have (special) joints in between the panels which also discolour and make cleaning more-awkward.

do they last a lifetime ?

In my experience, certainly not.
I have two separate makes still in use, one in an area resembling that which you describe.
It was advertised as having 10-year guarantee (or perhaps it was 20?) but I can assure you that I would not like to see the condition of polycarbonate in situ after 20 years - and this after less than 10 years, though at 10 it shouldn't be too bad.
Please be aware though that I live on the coast, where it certainly becomes brittle with age and exposure to the elements.

Honestly I would have to say it is choice and budget; I would personally still choose polycarbonate by preference.