Roof trusses: 600 or 900 centers

I’ve been getting quotes for roof trusses, and some are coming in with 900 centers and others 600.

There is a cost benefit in going 900, but I’m concerned whether that’s a wise choice.

Does 600 centers offer any benefit over 900?

Which do you recommend, and why?

tile or colorbond
provision for future solar panels or solar hot water

joejoemetoo
The trusses,Hold downs & Shear walls below will need to be designed by an Engineer
That is what is recommended by regulations.

It’s a flat kliploc roof.

We may add solar panels in future.

Not going with solar boosted hot water.

Our asked our structural engineer and he said he doesn’t specify the centres. Said the truss company’s engineers design the trusses to suit. I’m not sure about this.

More info required, steel or timber trusses, Flat Ceiling or raked, the bottom truss chord distances will also change your ceiling batten centres,etc,etc things to consider
You might want to read this
Slab heave is alive and well,watch out in particular the trusses.
MAKE SURE YOUR ENGINEER INSPECTS THE TRUSSES
hth

This is the case around my way. The engineer who designs the foundations (slabs, footings, piers, integrated retaining etc.) is not the same one who designs the frame and roof trusses.

Have you not noticed the shift of large engineering firms from the west to the east coast?
Their Services are all inclusive and cheaper...hth

Our house will be timber frame, flat ceiling.

Rather than me trying to guess your design variables why don't you put up a floor plan, site plan, elevation remove your address, designers name,etc, more info required.Also ask your designer for a BIM 3D Model as it comes in handy, theses days they can also be used for FEM Simulations though I doubt that your truss designer is that advanced.
OT, On the same design I also analysed Contaminant AirFlow

Is calculating rain fall and how box gutters handle the load part of FEM simulation? Apparently we need to show this too.

Sure you can FEM anything, you just need the equations (I digress, the big money is in Biomedical devices, drug chemical simulations,etc)
Rainfall & Stormwater Water flow can be easily calculated in a spreadsheet or as I prefer Google Sheets
The raw data comes from the BIM 3D Model and the internet; The more info you can get, the more valuable the model becomes, that applies to everything