Didn't both of those stories leverage existing sets, though? The Globe was filmed in a recreation of the original, which was already in operation as a proper theatre; and Pompeii was largely filmed on the existing sets of "Rome". Both episodes DID have great ancillary rooms, etc. that were constructed for the episode; however you are referencing historical locations, which on IMO are easier for a TV show to make accurate enough, versus various future-placed episodes which can look cheap and flimsy OR expensive and awesome. Who has done both in spades, under either producer.
Regardless, the buck DOES stop with RTD and Moffat, who have the responsibility of balancing creative control versus the budget they're given. I think their skill and experience as producers has as much to do with the physical look of the sets as the production designers who do the actual sketching and construction. Likewise, someone approved the use of an undisguised basement as a Dalek ship, or of whichever disused industrial location as the spaceship / prison / hospital planet of the week.
Mark
The Glode was filmed at the real Globe and only at night, every morning they had to clean it up and take down their lighting blimp for the theater's daily shows. And all tey used from the BBC including the TARDIS was shipped over and taken by lorry(truck) to the Rome set.
“Love's Labour's Won” was married to the preceding episode, season premiere Smith And Jones, to form the year's second recording block under the aegis of director Charles Palmer. It quickly became apparent that the scale of Roberts' script exceeded the other historicals made for the new Doctor Who series. To resolve this, the production team approached the management of the new Shakespare's Globe Theatre. Opened in 1997, this was a faithful reconstruction of Streete's original edifice, which had been destroyed by fire in 1613 (and rebuilt in 1614, only to be closed by the Puritans in 1642 and torn down in 1644). Doctor Who became the first television drama to be granted permission to film at the new Globe, although a requirement of this deal was tate recording could only take place at night; Roberts' scripts were duly revised to reflect this.
The first material recorded for “Love's Labour's Lost” involved the set for the Carrionites' lair, erected at the Upper Boat Studios. This spanned August 23rd to 25th, and was originally intended to include an elaborate swordfight between the Doctor and Lilith, which was excised only at the last minute when it was felt to be too impractical to complete. The production was then nearly dealt a terrible blow when it appeared that contractual difficulties would scupper the filming at the Globe Theatre after all. A complete rewriting of the script to relocate the action to the countryside was contemplated, but fortunately the issues were resolved in time for the cast and crew to leave Cardiff for their first location, Coventry in the West Midlands, on August 28th.