I am currently designing my first dungeons, and I've noticed that some objects (notably the NorRitalRoom, among others) have walls on the inside (as in, if you're in the room, you can see the walls) but no outside walls (from outside of the room, some of the walls are invisible). Obviously this was not a problem for gamesas or other modders, how do you fix this?

The rooms were designed to never be seen from the outside so the "outside" walls have no textures and are thus see-trough, you can see this everywhere in-game by using the console command tcl and moving through a wall and turning to look back. If you only see this from a place where the player should never normally get (i.e outside the playable area) it's not a problem. If you see it from a place that the player can access normally you have to fix it by placing another wall object so that it covers the missing bit.

Sigh.

Anyway, where are the ceiling pieces? I can't find them.

I can't find the NorRitalRoom pieces you are talking about (sp?) but most of the center areas are labeled ...Mid....and contain both a floor and ceiling section. Is that what you are looking for?

The "ceiling" pieces are actually floor pieces. You REALLY should do the level creation tutorial, or the kits are going to confuse the hell out of you. Trust me.

Actually there ARE Floor pieces with no ceiling...but no ceiling pieces with no floor. This makes it somewhat difficult to make an extra-tall room unless you make absolutely certain that the player can never see it from above the "invisible from the bottom" floor just below the ceiling, or use the cave kit which has standalone walls that can be rotated to make ceilings..

There are plenty of kit pieces that allow for making extraordinarily tall rooms.

really? If you can show me exactly how to continue the wall style of DweRmSmWall up to an arbitrary height, with the ceiling that goes with it at that height, with no blocking "extra ceilings" along the way, or floating floors, I'd be really impressed.

Mess around. The kit pieces provided to you are actually really good in Skyrim. (SO much better than previous titles!!!) You just need some imagination and you can make any shape room you want. Much like how you can use pillars and rocks to cover up transitions between kit pieces, you can use chunks of the Dwemer kit to make a giant room, you just need to expirement.

As stated by Alexander, with some creativity you can do just about anything. As for your specific request - you're using a Small Room kit. Try looking in the DweRmLg kit...

Totally different wall textures.

I wish they'd designed the kits so you could "Turn off" the ceiling or floor on the wall pieces for just that reason.