So it's clear. You do not need add ons to build dimensions. I myself do not use them to build but enjoy understanding them and using some things in them to make my game more time efficient.
In Dimensions, Dimension Toolbox and Dimension Tools took building of Dimensions to whole different dimensions, literally - though they do not have to be used for just building but also saving sets, or whole dimensions in case you would like to build on the PTS (Public Test Server) first to work out all your items or so you can reuse things you are extra proud of in future builds.
Magic Carpet We have three major Dimension Add ons the first being Magic Carpet which gives you the mobility to fly around Dimensions or use as scaffolding.
You will need an Ochre Rug to use it and it has also been updated in Dimension Tools as Tribal Magic to offer a smaller item to move on.
Offers extra capabilities to move, rotate, scale, copy and paste plus save sets. Dimension Toolbox has not been updated since 2013 but it is still used because it was the only add on for so long and many Dimensioneers have saved sets using this add on.
Dimension Tools Is the 2014 update to Dimension Toolbox and is capable of doing everything Dimension Toolbox can do.
Dimension Tools also added group moving item capabilities, using items straight from your bank, Tribal Magic as well as a ton of tweaks along with advanced features such as: Offset calculator, dome building settings, a word processor and French translation.
Working with the programmer who made Dimension Tools saw all guides for Dimension Tools placed on Rift Dream Dimensions and there are other great guides for Dimension Toolbox available on the internet but unfortunately both add ons are no longer being updated so which one you choose to use is completely up to what you want to use it for as both currently have possible glitches with lack of updates.