Where can I find a forum where builders are on it?

[Wherestheinstructions]

I’m mulling over an idea for replacing my raised decking and rather than waste people’s time getting them to come out and look, I was hoping to put my idea on a builders forum to get their opinions on it.
where can I find that place? Or are any Mumsnetters builders or husbands are builders??
my mulling is, my current raised deck is made from wood frame with composite boards. It’s not the best job as the builder turned out to be a cowboy and I couldn't afford to have it put right. It’s useable but I can’t see it lasting long term. We are south facing and the decking is warping/cracking in some places.
initially I wanted a steel frame but the quotes were at least twice my budget.
now my question is, I’ve seen steel frames used as a mezzanine in warehouses.
is there a reason I can’t replace my wooden frames used with one of these??
for clarity my raised deck is 3 meters above ground to allow us to walk out from our first floor. It’s also 6m x 4m .

any thoughts very welcome and yes all planning permission granted for the original work.

There’s a self build forum out there. Search for that and you should find it. Full of amateurs that can give you advice to start off with.

Diynot forum

Yes this. Was just going to suggest it myself.

Screwfix have a forum.

Second the Screwfix forum. A number of people there who know their stuff. Put it in the building sub forum and you’ll get some helpful advice. In terms of your question you will need to make sure whatever you use is suitably rated to span the void. Any reason why you don’t want to replace with wood again if the sub deck really is that bad? You can look up the span tables below, so assuming the joists are running on the 4 meter span you’d be needing 2 x 8 inch at 400mm spacing (might get away with 2 x 7). You able to inspect the sub deck? Why do you think it’s shoddy? Composite decking can expand and contract with seasonal changes and therefore it might be that causing cracking etc if it haven’t been given room to do so.

www.rightsurvey.co.uk/floor-joist-span-tables-for-surveyors-floor-construction/

To add to the above, if the decking isn’t bouncing / noticeably moving under weight then I’d suggest it isn’t likely to be the joists / sub deck. When you say couldn’t afford to put it right who is it that has said it is wrong, and what is wrong with it specifically?

Thank you, these are super helpful.
@NonmagicMike to answer your questions;

it came to light after me thoroughly inspecting the sub deck that the posts aren’t fixed, there’s a join on the beams with only screws. The boards have warped badly in a couple of areas, but it does get extremes of temperature out there.
some of the boards join over no support.
and I’ve just lost faith in it, but it’s so useful to our enjoyment of the house and garden it’s essential.

sadly I succumbed to the demand/coercion of the builder for payments, and then ghosted me when I gave him the ‘snagging list’

i had originally wanted it done in steel, but when quoted at £25k it was way out of my budget.
hence me seeing these steep frames for a mezzanine advertised and I wondered why can’t I use one of those?

Quite hard to picture without seeing. If it really is that bad then not sure I’d want to be 3 meters up in the air on it! The boards joining over no support is definitely a worry - composite very easy to break if it isn’t properly supported. Sounds like a disaster!