GoodMorning IES - Best way to create an accurate model?

[Puccini]

Good day to anyone who comes here,

I'm tasked with creating a model based off a plan and its not made too fit into IES geometry standards so as you can assume, I cant use the grid to ensure my geometry is clean and generally the plan is made by architects meaning its very messy with notes and the building structure is quite complex.
While constructing the building geometry I found if I stuck to highlighting the interior walls I couldn't get a full building model for the purpose of my TM 52 calculation, as there was simply a void where the walls should be. I have been advised that I shouldn't enable inner volume for this and that I should just start by cleaning up the geometry in AUTO-CAD ready for IES, which seems like a sure fire way to get it done but I would have thought that given that IES is a modern software, then using a DXF would be an option but perhaps there is another option.

So, for the purposes of a TM52 Calc, I am looking for a fast and effective workflow to building accurate geometry when processing a professional standard plan

Any input would be highly appreciated, thanks!