Rather than hijack Mike's thread, believe there is Hobbycraft near you in Dundee?
These are on offer, 5mm A1 size, Paper Covered, four sheets for £10.............they do stock other thickness and sheet sizes, something to practice on?
Buy White Foam Board A1 at Hobbycraft UK.
www.hobbycraft.co.uk
Ideal medium for making templates, see if the Plan will fit! Useful for making openings, for whether doors and windows fit/look right.
Internal walls to structures, infill, backfill, far to many uses to mention, no doubt other uses will spring to mind.
Whilst they are paper covered, with suitable covering of either PVA, and/ or using Plaster, Clay, Sand & Cement finish, suitably painted, will endure many years outside, even with the inclement British weather..........
Being thrifty..... keep a lookout for homes that are having Roof Line work done, often the installers are more than grateful to hand over the offcuts, saves them the hassle to dispose of them.....I have more than enough collected and stored to last me the rest of my time on this mortal coil!
PS: for those who jumped the gun, with statements of the bleeding obvious, try waiting, with a touch of courtesy until the posting is complete with the necessary information!
PPS: Suffer from a slow Internet Connection, therefore the need to save drafts and reddit in small bite size chunks is paramount!
And coupled with, took a chunk of skin of my right hand earlier in the day, which started to bleed profusely whilst typing the first draft, needed attending to!
So as the say patience is a virtue...................and as seems the norm for this Forum of late, 100 ways on negativity, but nothing positive!