[Ourgon]

Well, Sketchup itself fits the bill and can be used for free more or less indefinitely. I have used it to design an extension to our house, a 22x12 meter barn, a lean-to for my wife's horses, an octagonal chicken coop and much more. The drawings are accurate enough to use as templates for cutting wood to build trusses.

How to use Sketchup for as long as you need it? The solution lies in using Wine on Linux (or wherever you want to run it) to run Sketchup. Once Sketchup tells you the trial period is over - 30 days for Sketchup 2016, the version I use - you just wipe the relevant Wine directory and re-install Sketchup. Here's a script to automate this whole business:

   #!/bin/sh

   export WINEARCH=win32
   export WINEPREFIX=/home/username/.wine-sketchup
   export WINE=$(which wine)
   export sketchup_msi=/home/username/Downloads/SketchUp2016-x86.msi
   export gecko_msi=/home/username/Downloads/wine_gecko-2.40-x86.msi
   export vblank_mode=0
   export DRI_PRIME=1

   help () {
   echo <<-END
    use: $0 [-r] [-h]
   
    -r: reset sketchup (does a complete reinstall)
    -h: this help message
   END
   }

   sketchup_reset () {
    rm -rf $WINEPREFIX
    winetricks win7
    winetricks corefonts 
    winetricks vcrun2010 
    winetricks dotnet40 
    msiexec /i $gecko_msi
    winetricks win7
    msiexec /i $sketchup_msi
   }
   
   config () {
    winecfg
   }

   while getopts "chr" OPTION
   do
   case $OPTION in
   r)
    sketchup_reset
    ;;
   c)
    config
    exit
    ;;
   h)
    help
    exit
    ;;
   esac
   done

   $WINE "$WINEPREFIX/drive_c/Program Files/SketchUp/SketchUp 2016/SketchUp.exe"