I'm posting this as an answer because it has grown far too long to post in comments.
In short, the appearance of rural housing in the mid-eighteenth century varied according to where you were in England, and the nature of the local building materials available.
As with any other period, the appearance of houses and the living conditions in rural England in the mid-eighteenth century varied enormously across the country. The primary determining factor was the type and availability of building materials in particular locations (for example, cob construction was most common in the West Country, particularly Devon and Cornwall).
Timber construction with wattle and daub was certainly fairly common in many rural areas, as were thatched roofs, but brick had been increasingly popular since the Tudor period, and slate was used as a roofing material in those areas where it was readily available.
I'd recommend three texts if you are looking to try and understand the development of rural vernacular architecture in England. These are by no means recent publications, but they still appear as standard texts on the reading lists for many archaeology courses and are relatively inexpensive if you want to buy copies. Two of these are available to borrow from Archive.org.
- Villages in the Landscape by Trevor Rowley
This is a great high-level overview of the subject. You may find Chapter 6 The Changing Village, 1600-1900 to be of particular interest here. This is available on archive.org.
- English vernacular houses : a study of traditional farmhouses and cottages by Eric Mercer
This survey was commissioned and published by the Royal Commission on Historical Monuments (England). It has a useful breakdown by county, and includes illustrations showing typical floor-plans and building materials used in those areas. This is also available on archive.org.
- The Pattern of English Building by Alec Clifton-Taylor
As far as I can see, this one isn't currently available online. However, it is probably the most detailed of the three when it comes to explaining the geology of the counties and how that determined the building materials locally available for vernacular architecture. Of course, the appearance of the housing depended almost entirely on the materials used to build it.