New builds have low ceiling b/c of building regs. So even if you built your own home from scratch you get low ceiling heights (don't ask me how they get round it on Grand Designs). Houses from the '60's, 70's and early 80's are good modern bets b/c they tend to have higher ceilings and bigger rooms. New builds from the 90's onwards have smaller rooms b/c purchasers demand the kudos of having lots of reception rooms and en-suite bathrooms, so more rooms have to be carved out of increasingly smaller spaces.
I've never yet been in a barn conversion that felt 'right'. The upstairs spaces are often very cramped and you really need to duck down low to avoid banging your head. Plus there are usually mad restrictions on teh outside, even down to what you can plant, and an ugly view of a silo or falling-down tractor shed.
I loathe uPVC windows, ours are so naff and really spoilt the look of teh house from the outside. They don't look so bad from the inside though and at least I can open them easily, unlike the windows in our old cottage.