You need a USB portable version.
This happened to me also... (I spent weeks trying to fix it)
It will take a while (You need a few spare GigaBytes on your USB stick before continuing)

First, make a folder (Applications) this is the ROOT folder.
Then, (inside that) make your 'Documents' folder (to mimmic the Documents folder you would of had)
Also make a Game folder 'Command & Conquer 3' (to mimmic your program files folder)
Copy and paste the full content of your Command & Conquer 3 (including the MOD SDK folder that is in there)
Once this is done follow the steps bellow.

Right click and edit the BuildMod.BAT
Add and replace all lines with the bellow (Note that this is for the G:\ Drive, please replace 'G:\' accordingly):

@echo off
@echo Mod Name: %1
@echo Building Mod Data...
tools\binaryAssetBuilder.exe "%cd%\Mods\%1\data\mod.xml" /od:"%cd%\BuiltMods" /iod:"%cd%\BuiltMods" /ls:true /gui:false /UsePrecompiled:true /vf:true
@echo Building Low LOD...
tools\binaryAssetBuilder.exe "%cd%\Mods\%1\data\mod.xml" /od:"%cd%\BuiltMods" /iod:"%cd%\BuiltMods" /ls:true /gui:false /UsePrecompiled:true /vf:true /bcn:LowLOD /bps:"%cd%\BuiltMods\mods\%1\data\mod.manifest"
@echo Copying str file if it exists...
IF EXIST "%cd%\Mods\%1\data\mod.str" copy "%cd%\Mods\%1\data\mod.str" "%cd%\BuiltMods\mods\%1\data"
@echo Copying Shaders...
IF NOT EXIST "%cd%\BuiltMods\mods\%1\Shaders" md "%cd%\BuiltMods\mods\%1\Shaders"
copy "%cd%\Shaders\*.fx" "%cd%\BuiltMods\mods\%1\Shaders"
del "%cd%\Builtmods\mods\%1\data\mod_l.version"
@echo Creating Mod Big File...
tools\MakeBig.exe -f "%cd%\BuiltMods\mods\%1" -x:*.asset -o:"%cd%\BuiltMods\mods\%1.big"
@echo Copying built mod...
IF NOT EXIST "G:\Applications\C&C\DocumentsTW\mods" md "G:\Applications\C&C\DocumentsTW\mods
IF NOT EXIST "G:\Applications\C&C\DocumentsTW\mods\%1" md "G:\Applications\C&C\DocumentsTW\mods\%1
copy "builtmods\mods\%1.big" "G:\Applications\C&C\DocumentsTW\mods\%1"

Also please note that this is based on my own directories.
'Applications\C&C\DocumentsTW' is a directory I made on my USB stick.
I have E:\ F:\ and G:\ Drive versions to which I saved them manually under:
BuildModUSBE.BAT
BuildModUSBF.BAT
BuildModUSBG.BAT

I hope this is enough to get you started, however one last note:
You need to find CMD on your Windows 8 and copy it to your ROOT directory for C&C3 MOD SDK (do not create shortcut to CMD).

If you need more help go to:
www.moddb.com/members/genzool

I am active (this information valid for 5 years without doubt)