Repost because last time this question even managed to draw one downvote for whatever reason so if I did anything wrong please tell me...
So – I think we all have seen some stereotypical depiction of a Roman city / some random medieval town. Either way they might have looked at least somewhat accurate for their respective time periods, but what about the time in between?
Let's say it's about the early 8th century and I'm living in some larger town (I don't really dare to use the term "city" here) in Francia that had already existed in Roman times. How "Roman" does my hometown still look, are there any ruined buildings around or, dramatically speaking, would an amalgation of dirt huts surrounded by an old wall be all there is? Would I already be seeing buildings that look stereotypically "medieval"?
Martel was king of Frankia under the papacy of the Holy Roman Empire so you'd certainly see religious buildings at settlement centres that you would largely recognise in form today. Depending on the age of the settlement you may still see some standing Roman Empire buildings that remained in use although it was common practice to dismantle buildings and re-use the stone. It's very likely that recently built Holy Roman buildings like churches and monasteries would have such stone in them. You wouldn't see many ruined buildings as the stone would have been re-used, the wood would have been taken for fuel or rebuilding, and in a larger town the plot would have been reused almost immediately.
The bulk of the dwelling buildings would be built in wood and daub - more substantial than "mud huts" but not that far removed in terms of technology. You'd find that major streets would have ings or stones laid to preserve them and you'd recognise marketplaces and, at the periphery, farming buildings.
A built-up town would at least have a ditch around it and, where the money was good, a solid wall of wood or stone. "Bars" and gates would protect the entry points and collect fees for passage. All-stone town defences were unusual and would most often circle the rich core of a town with a further wooden wall beyond. Some places, such as Paris in West Frankia, would make additional use of geographic defences by building the core settlement on islands and defending them with bridges and river chains/ropes. The less valuable, and therefore less impressive, parts of the ville would sit outside the most heavily defended core.
To summarise: if you visited a large town with several thousand inhabitants you'd recognise the layout, you'd start to see impressive religious and burgh buildings in stone and wood, you might still see Roman Empire buildings in important centres, but you would still see many "basic" buildings with wooden frames that rose one or two storeys.
Sources:
Paris - an architectural history; Sutcliffe A; 1993
Medieval and later settlement around Chassenon; S Turner, J Webster, M Duggan; 2011
Art and architecture in medieval France; Stoddard W; 2018