The plans for Idris were originally published in 16mm Today. They are available for download in DWG (Autocad) format. If you have a CAD program which supports DWG, then I suggest this may be the best option to try.
The DWG plans are held in file indrisplndwg.zip.
Alternatively, if you do not have a CAD program, the plans can be downloaded as either as a PDF file (courtesy of David Bousfield) or as individual GIF files by clicking the links below. I regret that the text and dimensions are more difficult to read in the GIF versions, but I believe this version of the plans is still usable.
The individual sheets are:
