Payload: 5 kgs
Flight Time: 45 - 55 minutes.

It will cost you a bomb..that is for sure :p .  You would need U8 motors and 26 inch props and lots of them.

5Kg payload and 50Min flight time
Can this be called hobby or is it for Military use ?
How ever, Allthatido(don't know your real name sir.) is right.

Let me put this way:

System should be capable of lifting 5 kgs.
Total Flight time should be 45 - 55 minutes with or without payload.

is this 5Kg all up weight or just the payload ?

all up wait : means the total weight of aircraft + payload.

its only payload..

Whats your budget? Are you already a multicopter pilot?

No limit on budget...
Piloting not needed.

Well, then I could say it can be done (as you said no limit on budget )
But what d'you mean by no need of piloting    is this for safe keeping in a shelf after building ? Some one have to fly it one day, isn't it ?

Please don't worry about piloting.

Just post average cost, if it can be done...

Here i found this data from RC groups,
http://www.rcgroups.com/forums/showthread.php?t=1372744

with some mods on that and may be an Octo, you can definitely achieve that payload carry capacity and flight time.
if you want I can search and find a suitable platform.

Rough calculated an AllUp weight of around 10 - 12 Kg.
You could go for an Octacopter for more stability.
So AUW be 12Kg, each motor should provide more than 3Kg Lift.
Let me search.

What is your intended payload? It can definitely be done with limitless budget. Use t-motor electronics, custom made CF frame, some A-spec nano tech batts, cf props ofcourse and a dji a2 or wookong flight controller. I would say around 4-5 lakhs. About $8000+.

Thats a good price.

How much does it take, for someone to build it and deliver.

What is your time frame ?
As 4-5 lacks is a good price for you it's easy to build one.
p.s not my business, still can't wait to ask, what is your purpose with this heavy lifter?

4-5 Lacks is not at all needed if you know where to and how to source parts.

What time you can deliver?
Purpose is confidential.

4-5 lacks ,woah thats a nice budget you got!!!
can you share the purpose of building this expensive machine?
and do you want the multirotor to have higher stability or higher motion??
i think this is the thing you are looking for:
you can buy it ,its 6,999$: http://onlyflyingmachines.com/product/ofmgq8octa/
regards
rohan

Rohan, his purpose is CONFIDENTIAL .!

OFM products are good, but the link you gave, can it load 5Kg on it's belly and keep it's wings spread wide in air for 50 min.s
If yes, that's what this guy is looking for.

i didn't read that reply(was typing at that time)
regards

That's a nice platform...

I am looking for something smaller in size...

it can lift 6-7 kg ,you can add a couple of batteries ,will increase the flight time.

How confident are you, in terms of reliability of such a build. Have any of you really built such platforms in past.

then ,i will suggest a X8 configuration,it is a quad in which you mount 2 motors on one arm so the as in a octa the size increases because there are 8 props ,in a X8 there will be just 4 up and 4 below so the arm size can be reduced.

well i have never build such a machine but i think there will be a few people who would spend that much money on a project.
but you should ask alishanmao ,the guy is a lot experienced and if you dont want to build the multirotor yourself ,maybe he can build it for you.
regards
rohan