You have no mod.xml, your mod has no name (your folder structure is wrong),
or you're trying to build the mod wrong.
It's probably the last one but I'll go over all of them.
#1. As discussed in the documentation, Mod.xml is the file that tells the compiler everything in your mod that needs to be built for it to work. In Mod.xml you list the files that should be built into your mod. In your case you want the .xml files that correspond to the different Tiberium textures (documentation also talks about textures in the sample mod section).
and/or
#2. Your mod has no name (meaning the folder structure is wrong.) In the MOD SDK\Mods folder you make a new folder for every different mod you create. The name of the folder is the name of the mod. It can't be longer than 15 letters/numbers. Inside the "yourmod" (or whatever name it is) folder you need to make a data folder. So that's MOD SDK\Mods\yourmodname\data
Mod.xml and all your other .xml code files go in here (yourmodname/data)
except for art files. Art files usually go in the MOD SDK\Art folder inside another folder that is named after the first 2 letters of the art file. So for example, all of the textures you're working with start with tiberium so they (and their .xml files with the same name) would go in MOD SDK\Art\ti
and/or
Which brings me to #3. If I had to guess, you're double clicking on the buildmod.bat file which isn't the correct way to start the compiler. You need to open a command prompt and navigate to the MOD SDK folder (Again, all of this rudimentary stuff is explained in the documentation so read
all of it).
Then type "buildmod.bat yourmodname" only without the quotes and hit enter. Then if everything is right (you have a mod.xml in the correct folder, everything else is in the right folder, and there are no errors in the code) it will build your mod and copy it to your My Documents\Command & Conquer 3 Tiberium Wars\Mods folder inside another folder with the same name as your mod.
Now of course it can be a pain in the butt to navigate manually to the MOD SDK folder every time you want to compile the mod, so you can
download this little "Power Toy" from Microsoft (only if you want to) that will let you right click on your MOD SDK folder and "Open Command Window Here." Or you could set up a shortcut that will automatically compile your mod when you double click on it but I don't know how to do that. Or finally you could download an
altered buildmod.bat or a simple graphical buildmod to make it easier for the command line impaired.
Finally you need to make a .skudef file (Just make a new .txt file and rename the extension to .skudef)(You need to turn off "Hide file extensions for known file types" in your Windows Folder Options) named YourMod_1.0.skudef (where of course YourMod is whatever your mod name is, and _1.0 is whatever version of the mod you want it to be) Inside the Skudef file, you will put the following text:
mod-game 1.9
add-big YourMod.big
This tells the game to launch the patch 1.09 version of the game, and to add the data from Your Mod into the game.
And then you launch it from the C&C3 Control Center.