What you need to be aware of is the safety requirements of the game that you are planning to play but these are fairly standard because most makers want to be able to work across different systems as there aren't that many LARPers so a maker wants to be able to sell to as many of them as possible.
The standard construction is a polycarbonate or carbon-fibre core with a high-density closed-cell foam ( plastazote or similar is typical ) for the shape of the weapon and latex surface layer. You may need to use softer foam for anything that is likely to be too risky with the denser foam types - tips on stabbing weapons, for example.
If you work with those materials and you make sure that you're aware of the safe distances between the core and the edge of the weapon, you should pass weapons check at most reputable systems, but until you have made a few weapons using a conventional approach it would be unwise to get too experimental- any weapon that doesn't have enough give in the materials will not be allowed on the field in most systems. If the structure crumbles then within a few blows you will be hitting people with the core, or with a core in a latex bag of foam dust, which is likewise unsafe.
The weapon in your illustration looks like a cosplay prop rather than a LARP weapon - the wooden core designed in two pieces, use of expanded foam and amount of exposed haft all suggest that it would not be combat safe- if it was being shown as a LARP weapon that is probably a mistake on the part of whoever posted it. You could make a LARP weapon that looked like that, but you wouldn't use that process.
