It comes down to aesthetics vs cost.
You can still get "rosemary" plain clay tiles. Redland do them. To re-roof with these will cost twice as much compared to modern interlocking concrete tiles. You need 60 rosemary tiles per square metre. Wheres with concrete interlocking tiles (large format) you need 10 per square metre. They are also more labor intensive to lay.
Per Metre, rosemary tiles are actually heavier than modern concrete tiles, so you should not have a problem with weight.
It is when you replace slate (which is very thin and light) with much heavier concrete tiles where people have usually had a problem.
So:
Have your neighbours replaced their tiles yet? Are you bothered about matching their tiles? Terraced houses are usually all mismatched anyway these days.
If cost is not an issue, (and Rosemary tiles would look the best) go with a like for like replacement.
If cost is an issue, you can go for large format plain tiles, which look like supersized plain tiles. Or a Roman (wavy) tile. Whatever look you prefer.
A halfway house would be sandtofts 20/20, which is an interlocking plain clay tiles (slightly larger) but you still only need 20 per square metre. There is also Redland concrete duoplain, which is a fake plain clay tile look. It is actually a concrete tile, similar in size to the sandtoft 20/20.
So, like I said, it is aesthetics vs cost!
