Okay so i'm planning on use the RoHT mod, but I also want an upgraded Tel Uvirith, preferably an upgraded Tel Uvirith with a town. I know that RoHT can be used together with Uvirith's Legacy. But apparantly Uvirith's Legacy can be used together with Building up Uvirith's grave through the Building up Uvirith's legacy mod.

So what I want to know is, will using all of these mods together muck up my game because they clash? Or will it be fine?

In short is it fine to use

Rise of House Telvanni: http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=4449
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Uvirith's Legacy: http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=5997
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Building up Uvirith's grave: http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=5730
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Building up Uvirith's legacy: http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7736

Don't use BUUG together with BUUL (since the latter was made to completely replace the former, aside from a few features) and you should be ready to go. As far as I know there are no compatibility problems, since UL and BUUL are obviously meant to be run together and RoHT is compatible with both (there are patches for Uvirith's Legacy which fix some minor quibbles). I'd add LGNPC Tel Uvirith as well, if you aren't using it already.

As the above poster says, BUUG and BUUL are functionally the same exact mod, but BUUL has the interior parts removed to ensure compatibility with Uvirith's Legacy.

I'm not certain of any compatibility issues with any of the mods and RoHT, but I haven't used RoHT in ages, so other people will be better off than I will.

Don't forget LGNPC: Tel Uvirith! It's awesome and also compatible.

Uvirith's Legacy and Building Up Uvirith's Legacy are compatible right off the bat. In fact, I recommend BUUL over BUUG. Though you do lose the ingredient nest, you'll get something that acts just like it (and with UL's MWSE patch is compatible with mod ingredients!) and there's a ton more added to the tower. Uvirith's Legacy and Rise of House Telvanni require a compatibility plugin, which is downloaded from the same page as RoHT. All three and LGNPC Tel Uvirith run perfectly together, as long as you use the main version of TU and not the version marked for Uvirith Inside.

I use all four in my setup. Uvirith's Legacy is a little buggy but otherwise they all play nicely.

I'd recommend running http://www.gamesas.com/topic/1167004-relz-mlox-a-tool-for-anolyzing-and-sorting-your-load-order/ against your load order. It's got all these mods in its rule set.