Hi,
I've had a lot of experience 3D printing from Revit.
You've picked a challenge - 3D printing from Revit consistently is difficult with a $90,000 3DSystems Projet SDM/Inkjet machine... it is even trickier with an FDM machine!
That said, it is possible. You will need another piece of software other than Revit - if you don't have access to something heavy-weight like 3DS Max, then I suggest Sketchup Maker. You could use Blender, but I have no experience of that application.
First off - your terrain. Revit will expert a single triangle-mesh for your terrain - this item is NOT a solid. You can however force Revit to create a basic 'box' from the terrain though - use the Section Box setting from the View Properties, and slice your terrain so you can see solid sides to it in the 3D view. When you export this you will get vertical 'sides' to your terrain. You will need to add a base poly however.
Which brings me to - leaky polygons. Revit will likely produce a lot of these, especially in your terrain, and these will cause any slicer to simply skip that object, or do something really strange.
You will need to use either the STL-Check modifier in 3DS Max or the similar function (it might be an extension) in Sketchup to identify these objects with 'holes'. You will probably have to fix these by hand
The next important point is to know your print scale, and know your print-head minimum size.
My example is a Flashforge Creator Pro, using a 0.4mm nozzle. The minimum object size I can reliably print is 0.8mm ( 2 x 0.4mm) - any thinner than this and it is one one extrusion layer thick and likely to fail. 0.8mm is just printable. Just. To be safe, lets say 3 x 0.4mm = 1.2mm
So taking our minimum printed object size of 1.2mm, lets say we print at 1:100 scale - the smallest printable object in you model will have a minimum size of 120mm! Thats thicker than most standard walls, and far larger than any delicate furniture or railings! In my printer, 1:100 would give me a model roughly 20m x 15m x 15m - ok for a house, but for anything else, I'll need to use a larger scale - and my minimum thickness will only get worse!
At 1:200 - minimum size is 240mm - as thick as blockwork walls.
At 1:500 - minimum size is 500 x 1.2 = 600mm !
Unless you're printing at 1:20 (!) I suggest you turn ALL of the following categories OFF - Doors, Windows, Railings, Gutter, Eaves, Furntiure, Specialty Equipment, Mechanical - etc. Anything with fine detail is just not going to work.
Now you need to ensure your walls are at LEAST equal to your 3 x layer minimum size, and your slabs & roof should be probably 4 x minimum size otherwise they will sag. Also beware that your maximum bridge distance is probably 50mm or less, so you might need to add internal walls to help support the roof. Avoid large areas of solid fill as this will eat your filament & take ages to print - it's easier & neater to use internal 'support walls' in Revit than to add support in Simplify 3D. For external areas you won't have a choice - any cantilevers over about 6 x min layer size will need support, and any large bridges will need it too.
it all sounds complex & difficult, but with care you can produce exceptionally good models with FDM from Revit - but you have to work with the limitations of the print process and manage your clients expectations for the result.
I use prints from Revit mostly for massing / shadow studies of masterplan scale models - so I work with Masses on a Topography at very large scale 1:1000 or above. I have done successful prints at 1:100 scale, but they take AGES to print as anything at that scale is likely to fill the entire print bed.
Good luck with your prints from Revit!
