Hi Thinking of building but would need to deliver a small payload, any ideas where to begin?
What’s the payload
Begin in Columbia and end in USA? 
Sorry, I don’t have a proper answer for you. I’m sure a more sensible knowledgeable member will be along to help you soon.
In the meantime, some more details might help.
Fixed. 
A tool that dismantles R#^*€ian tanks instantly and very efficiently….
Tarot have a good range for mid lift.
If you need really heavy lifting then look at T-Motor motors with carbon fibre props bigger than 15”
For calculating lift with a variety of engines frames, props and kit eCalc is a very useful tool.
You could either go the semi built route - take an S900rame and motors then add battery receiver and controllers (hint: I know someone only inches away from this keyboard who has a couple that could be for sale) With an FPV camera for visuals the whole underbellt is clear for whatever payload and release mechabism you wish to fit.
Slightly more complicated is selecting motors and ESCs and matching to a frame - bpoght in or homebuilt. As always follow Colin Chapman’s design philosophy of “Simplicate and add lightness.”
Best thing is to work out the weight of your patload abd release setup and the area it’s going to take up. Find a frame or a semi-built that suits those dimensions. Use eCalc to run the numbers for different motors, props, batteries and other kit - it has a very good database of components and their weights.
You also need to consider how long you want the aircraft to fly and for how far. Again eCalc will help you there.
If money is no object then take a look at FoxTech - loads of specialized aircraft there
https://www.foxtechfpv.com/naga-pro-coaxial-octocopter.html
https://www.foxtechfpv.com/thea-140-hybrid-pro-industrial-drone.html
Although those might be a liitle too big …