How do people make such flawless floors & ceilings?

First of all, I love that avatar. Which means you are going to get my expert help. :squirrel_eyebrow: Shutup you stupid squirrel. Sorry.
You want to set up some nice, flat boxes on the ground, to high you want the ceiling to be. Place the ceiling panels exactly in place, and make sure it's perfect. For multiple levels, just add boxes to the second level.

 

Try using the interlocking objects method. It's very useful and very easy.

 

in forge what I do is:

set boxes at the heights you want. Make sure all are flat. Make sure they are close enough so that a wall placed on them will not tilt.

start with your first double wall, usually I have it so that a double box is at each end of the wall.
double check to make sure that your second double wall, placed on either side of the 1st, has support under it.
place that one

these should start interlocking pretty easily. Using the wall brackets to line things up makes it simple.
then later on delete the boxes

 

As Nemihara said, use straight edges to line up your objects perfectly. Like in real life you require a ruler to make things perfect. Double boxes work great, if you don't have any of those fence boxes are also really good.

 

It also helps to have a certain amount of OCD when making maps that require the use of straight walls and floors. if something's not perfectly right, don't just leave it there if you're planning to build off it; it'll screw up your stuff down the road. Also remember--Foundry is not perfectly symmetrical. The "Base 1" side is about a half-square (on the floor) bigger than Base 2. Don't forget about that, it'll cause you major headaches if you plan a map that needs those areas to be symmetrical. Personal experience there.

 

How Do People do it?

 

Weediercola, please read the posts before repeating the thread title...

 

If you own more than one controller, sign in a temp profile or a few to help with object alignment. Sometimes all you need is the right perspective(s). Precise object placement can burn up a lot of your time, remember to prioritize which objects need precise placement now and which can be cleaned up later: it sucks to have to trash 30 minutes of work because you've thought of a better design.

 

I would second that. A good tip for efficient forging.

 

i always sign in a guest account to get a better angle view of everything. I really use a combination of the methods stated here, and always INTERLOCK.
just take your time and don't blow through everything.