Layers will work if you can put each variant on a single layer —if you want to show site plans, architectural plans, furniture plans, sections, models, renderings, for each variant, and need several layers for each variant and specific combos and views (say, 'plan') for each, it will be crazy. Also layers require you to mess around with layer combinations, which are best kept as standard as possible.
A more powerful and simpler approach would be to have the existing building on a file (let's call it EXST), and create a new file (say VAR01, VAR02…) for each variant, which has the existing building hotlinked into it, all stories and model elements and presentation views and layouts created, etc. For VAR02 you duplicate the VAR01 file, and start work right away —no fumbling with layers or views or layouts or anything. You can go on indefinitely and create 20 variants (you create variants just in case, every time you want to try something) with no additional setup work.
If the existing building model changes, because you want to add additional detail, got a new survey, or decided you'll tear down some part, you just modify EXST and update hotlinks on the variant files. If you decide that some parts of the existing building will be torn down with some variant and not with others (keep a full model of the existing building as a backup somewhere just in case), those existing parts which will not show in all variants need to be modeled in (transferred to; copy-pasted into) each variant file as required, and removed from EXST.
Layers, views, layer combinations, are kept standard. If they evolve, you just transfer them across files with Attribute Manager. You are building on your standard, instead of creating ad-hoc layers and combinations-views for a single presentation. And your renovation filters still work for renovation status views, for each variant.
