Ya know, you shoudln't really have used the customdev folder.... you should have made a new one with a unique name, like: team fortress 2\tf\materials\poopster101
Edit: just checked it out, for future reference most TF2 textures are 1024x1024.
-These plates seem too large with no scaling so I've reduced them to 0.12 rather than 0.25 and they look quite nice. (definatly in keeping with the TF2 style

)
-In future I'd make each plate unique, or at very least make a basic plate then copy it so it tiles then edit each one to make it unique.
-I loaded it up in photoshop and applied the 'offset' filter, this is because the seams on the texture don't match up with the edge of the texture, so if you have a standardly sized wall with this texture on, the plates don't start at the floor and end at the ceiling, they should (and do with just a little shifting) I've modified them, but not enough for you to worry about

if you want my slightly modified one (I also ran it through crazybump to get a normalmap) then just say.
-For your next texture, make a ceiling! a ceiling! there are barely any textures that are specifically ceilings.