Starting out, You're going to want to find where you want your roundhouse, and make sure you have the space for one (The total diameter of my roundhouse is 95m-100m at the rear of the actual buildings)

So you've found your spot, and have your line coming in, Now place your roundhouse where you want it and delete that incoming line. I like to use the cross sections to mark things, so that's what we will be using.

Place a cross at the ends of your round table. Like so :

Now I'm going to be referring to the sides as North South East and West with south being your incoming line (I add the actual incoming line in later shots to better show this).

So In order to mark the East and West lines, you could do 1 of 2 things :
1 - Eyeball it.
2 - Delete the table. Then from the North cross, bring a dead straight line in towards the centre by 6.1m and place a cross :

Then replace the table from the South cross (Its home placement) And Rotate the table until it lines up with that centre cross (Add the East and West marks here) :

So you have your cardinal directions, lets make a grid to find our ordinal directions (We learning compass words today conductors!)

I've added a line to the southern cross (Your incoming line) to make getting your bearings easier

The grid is really simple, On each cardinal add 2 crosses to the left and right so you have a 5x5 of crosses :

Delete the table, and using the spline tool, connect each of the East and West sides :

Do the same with the North and South sides :

Now remove the extra crosses we added earlier so we only have our cardinals remaining :

And finally add the table back to its home location (The southern cross) :

Now we get to the reason I don't like eyeballing this without a grid. Lining up your ordinals will require you to walk from end to end checking that the triangles created are all of "equal" size.

So start off by rotating the table to your first ordinal direction (I'm doing NE and SW) And check your triangles :

There are 3 sets of triangles to check and they should all look relatively the same.
Once you've checked them, place your crosses and make sure they look even :

Now repeat this for your other ordinal directions (NW and SE) :

Now its time for the Half winds! (More compass words!). This is where the reason we haven't placed our lines to measure out our Train sheds yet. We need the crosses to have something to eyeball off of.

This is where my descriptions may get confusing and I would suggest messing around with your table until you get the same result as what I've provided and can understand what I mean.

So we are going to rotate the table until it looks to be in a half wind location (NNW and SSE) :

Then you'll need to understand my poor logic.

When you are on the left side of a cardinal, use the left rail to line up your centre.
NNW, ENE, SSE, WSW are left side.

When you are on the right side of a cardinal, use the right rail to line up your centre.
NNE, ESE, SSW, WNW are right side.

The way you are lining this up is to make sure the (left hand for this example) rail is clipping into a grid rail like this :

Close up :

Then you can place your crosses to mark the location :

AND TO TRIPLE CHECK!!
To make sure it was indeed correct the cross should clip into the crosses on either side equally :

Left side :

Right side :

As you can see the clipping is even.

And then you just need to repeat these 6073 steps for the other half winds and :

ET VOILA!

The Indexing is complete!

Right, So you have your index round table and have learnt some new words for a compass.

Now its time to learn how you could use this to make a roundhouse. Because of how much fiddling and personal preference this takes, I'm not going to be as thorough in this section.

To start out, We remove the grid! (I removed the table to make it easier, place it back after the grid is gone, again from the home connection, Southern Cross) :

From here, We can do 1 of 2 ways :
1 - Rotate the table to each indexed location and delete the cross, then add a 14.9m-15m (It takes some time to find out which length you need but the 0.1m does make a massive difference[Starting with the longer, 15m is your best bet]) Straight line out :

2 - From each of the indexed crosses, take an 11m-11.1m (same reason as before) straight line out :

For my personal table I took the long route and did option 1, but for the rest of this example I will use option 2 (With an 11.1 starting measurement).

From here, go to the end of your North line (Important for correct spacing[Clipping]) And Pull out your desired colour of shed (I'm using brown to see the beams easier on the stupid snow) and centre it flat on the ground at the end of the embankment of the track :

Now continue to the left or right side and do this again, paying attention to how much it is clipping into the side of the first shed :

The Peaks of the sheds should look nice and even, essentially pointing into the window of the next shed :

Getting the spacing correct, and clipping, and length of track to use takes some messing around, and you may want a more spaced out clipping free build, its up to you, but it does take time.

After you are happy with your placement, Repeat this on the other side :

And once you are happy with that placement, repeat this for all your sheds (My personal roundhouse as an example) :

At this point, you may be asking yourself "But Jax, How do we connect the lines?" And that is a good question, I have my own way of how I like to connect them, and you may not like it.
The only other way i could think to do this would be to index an off-centre 32 point compass, and I am not about to try and figure that out, I have Lines to build, and fires to stoke .

So I'll show you my way.

This'll be fast and dirty, much like my Montezuma up to the coal mine (Joy riding only).

Start by removing the 11m sections leaving only the crosses
(If you used the 15m measurement skip this step) :

Now for context :
Left Rail on the round table to the right rail on the cross (Or 15m length)
Right Rail on the round table to the left rail on the cross (Or 15m length)

Line up the corresponding rails so they look like this : (Left rail - Right rail)

The then run a spline to that side of the shed :

And repeat for the other side (Right rail - Left rail) :

And the repeat all of that for the other sheds! (Gotta love the touchy rotations of the round table!) :

After all that pain and suffering, You should end up with this! (Personal Roundhouse as example) :

And there you have it! A perfect(ish) Roundhouse! Now you can mess around with using different rails and embankments as decorations ect, Im not going to get into that as I like my plain roundhouse for the moment.

I hope you managed to follow this guide, and got your own Roundhouse all set up now!

Ahhh .... Choo choo?