How pretty do you need it to be? Is it going to be seen from the inside, outside, or both? Make sure you're fully versed in the fusing of objects, because it can get complicated. The best way to start is to build an octagon out of vertical boxes to serve as the 'base' of the dome. I'm going to assume that you want to make it look uniform and will use either the single walls or the fence gates. Most likely you'll use whatever kind you choose up, so make sure you can use something in its place for anything else you're doing. I made a dome using bridges on a map a map I never published, because it ended up being the coolest part of the map. :-/ Good luck.
It's going to be seen inside and the outside. This map is going to be called Control Room. Gametype: TS, Assault, CTF
hmm, the more that I think about it, using walls won't work the same way the bridges did, especially to make it aesthetically pleasing to both sides. And you'd have to use both the regular walls and the fence walls, which would end up being a pretty big dome. I don't know if that will fall in line with what you're going for. I don't want to give you any bad information, so I may mess around with this concept tonight and get back to you. If anyone else can help you more quickly, though, go for it. But try starting with making the octagon like I was saying and see what comes up for you. I'll be interested to see what you build.
Sounds like a lot of trial and error. The only way i would know how is just to start with larger objects at the bottom, forming a circle or octagon (as squidhands suggested). Then use increasingly smaller objects as you build up the wall, that tilt at increasing angles inward the farther you go up until it is complete. You might have to make two layers to fill in the gaps. Also interlocking objects is recommended if possible. Other than that, the only thing i could do to help is try it myself, but if i do that, then i have essentially just done it for you. It sounds like a nice challenge. I could try to make it for you if you like. If so, how big do you want it?
Well making a round surface out of flat surfaces is impossible, so basically you would want it to be like a golf ball, many different sides put together
Actually nearly every "round" surface you see in a video game is composed of "flat" polygons. Also, ever hear of a geodesic dome? The challenge is how to do this with the limitations of Forge/Foundry. I think it is possible, but it may take a master Mason to make it happen. Where is Coolant when you need him?