After a certain update for NMS, i couldn't find the cubewindow (single wall) to be available anymore.
First i thought it was removed but this is such a crucial item in basebuilding (imo) so after browsing through some .Mbin files
i found that it was just not listed in the unlockableitemtrees.mbin
So i've re-added it.

this changes are made in
UNLOCKABLEITEMTREES.MBIN

Located in METADATA/REALITY/TABLES/...

I don't know how ot create an .lua script
But the lines that needed to be added are below.

Search for cubewindowoval
now you should see,
.........
<Property value="GcUnlockableItemTreeNode.xml">
  <Property name="Unlockable" value="CUBEWINDOWOVAL" />
  <Property name="Children" />

Copy and paste the lines below in your .MBIN/.EXML file
right below the line with "children" from the one above!

</Property>
<Property value="GcUnlockableItemTreeNode.xml">
  <Property name="Unlockable" value="CUBEWINDOW" />
  <Property name="Children" />
</Property>


So basicly the whole section where the line is in, comes from this

</Property>
 <Property value="GcUnlockableItemTreeNode.xml">
     <Property name="Unlockable" value="CUBEGLASS" />
     <Property name="Children">
  <Property value="GcUnlockableItemTreeNode.xml">
    <Property name="Unlockable" value="CURVEDCUBEROOF" />
    <Property name="Children" />
</Property>
  <Property value="GcUnlockableItemTreeNode.xml">
    <Property name="Unlockable" value="CUBEWINDOWSMALL" />
    <Property name="Children" />
</Property>
  <Property value="GcUnlockableItemTreeNode.xml">
    <Property name="Unlockable" value="CUBEWINDOWOVAL" />
    <Property name="Children" />
</Property>

to this (you can also copy and paste this whole section below
be sure to paste onto the same lines so the whole section get's overwritten correctly!

</Property>
 <Property value="GcUnlockableItemTreeNode.xml">
   <Property name="Unlockable" value="CUBEGLASS" />
   <Property name="Children">
 <Property value="GcUnlockableItemTreeNode.xml">
   <Property name="Unlockable" value="CURVEDCUBEROOF" />
   <Property name="Children" />
</Property>
  <Property value="GcUnlockableItemTreeNode.xml">
    <Property name="Unlockable" value="CUBEWINDOWSMALL" />
    <Property name="Children" />
</Property>
  <Property value="GcUnlockableItemTreeNode.xml">                   
    <Property name="Unlockable" value="CUBEWINDOWOVAL" />                   
    <Property name="Children" />
</Property>
  <Property value="GcUnlockableItemTreeNode.xml">
    <Property name="Unlockable" value="CUBEWINDOW" />
   <Property name="Children" />
</Property>