For hospitals in the Highlands of Scotland see www.historyofhighlandhospitals.com. Jim and Stephen Leslie have researched and written on hospitals in this area, and have published booklets on the hospitals on Skye, and in Lochaber and Nairn, with another on Inverness due for publication in 2016.
Peter Higginbotham’s http://www.workhouses.org.uk is a brilliant database of poor law buildings in Britain
National Library of Scotland has a wonderful collection of maps which can be accessed online http://maps.nls.uk
SCRAN is a subscription site, although much can be viewed free of charge. http://www.scran.ac.uk
The Royal Commission on the Ancient and Historic Monuments of Scotland’s site has a wide collection of photographs and architectural drawings as well as site records http://canmore.rcahms.gov.uk
ScotlandsPlaces has many digitised documentary sources, including OS name books and some Medical Officer of Health Reports amongst others.
Our NHS Scotland has an overview of the establishment of the National Health Service http://www.ournhsscotland.com/history/birth-nhsscotland
University of Dundee Archives: Hospitals and Medicine adminstrative and biographical histories histories http://arccat.dundee.ac.uk/dserve/dserve2/history/history.html
A comprehensive list of former asylums in England and Wales with varying accounts of their construction history can be found here http://studymore.org.uk/4_13_ta.htm
Urbex folks post loads of photos of abandoned and derelict hospitals, one really interesting website I came across recently is this one http://thetimechamber.co.uk/beta/ it covers some former English asylums, and other building types as well.