[ketakevin]

Got it running now. However if you're standing directly in front of a wall it doesnt work as expected, maybe one of you guys knows a solution for this?

If someone cares about the working plugin look at this

#include <sdktools>
#include <sourcemod>

public Plugin myinfo =
{
	name = "Mass",
	author = "ketakevin",
	description = "sourcemod port of the spray_distance_to_floor amx plugin by exolent",
	version = "1.0",
	url = "177 views"
};

/**
 * Called when the plugin is fully initialized and all known external references 
 * are resolved. This is only called once in the lifetime of the plugin, and is 
 * paired with OnPluginEnd().
 *
 * If any run-time error is thrown during this callback, the plugin will be marked 
 * as failed.
 *
 * It is not necessary to close any handles or remove hooks in this function.  
 * SourceMod guarantees that plugin shutdown automatically and correctly releases 
 * all resources.
 *
 * @noreturn
 */
public OnPluginStart() 
{
    AddTempEntHook("Player Decal", PlayerSpray);
}

public Action:PlayerSpray(const String:szTempEntName[], const arrClients[], iClientCount, Float:flDelay) 
{
    new client = TE_ReadNum("m_nPlayer");
    if(IsValidClient(client)) 
    {
		decl Float:start[3], Float:angle[3], Float:end[3], Float:normal[3];
		//Getting clients eyes position
		GetClientEyePosition(client, start);
		//Getting clients aim direction
		GetClientEyeAngles(client, angle);
		
		//PrintToServer("player position x: %.1f, y: %.1f, z: %.1f", start[0],start[1],start[2]);
		
		//Tracing the players aim...
		TR_TraceRayFilter(start, angle, MASK_SOLID, RayType_Infinite, TraceEntityFilterPlayer, client);
		//...until it hits a wall and saving the end point
		if (TR_DidHit(INVALID_HANDLE))
		{
			TR_GetEndPosition(end, INVALID_HANDLE);
		}
		
		//PrintToServer("aim location x: %.1f, y: %.1f, z: %.1f", end[0],end[1],end[2]);
		
		decl Float:vecPos[3], Float:height;
		new String: cname[30];
		//Tracing from the end point...
		TR_TraceRay(end, {90.0, 0.0, 0.0}, MASK_PLAYERSOLID_BRUSHONLY, RayType_Infinite); 
		//...down to the floor and saving the new end point
		if(TR_DidHit(INVALID_HANDLE)) { 
			TR_GetEndPosition(vecPos, INVALID_HANDLE); 
		} 
		
		//PrintToServer("vector values x: %.1f, y: %.1f, z: %.1f", vecPos[0],vecPos[1],vecPos[2]);
		//Calculating the spray height relative to the floor
		height = end[2] - vecPos[2];
		//Getting the players name
		GetClientName(client, cname, 30)
		//Output players name + spray height in the chat
		PrintToChatAll("[Mass] %s hat in einer Hoehe von %.2f gesprueht.",cname,height);
        //TODO: calculate spray height above the floor from three given vectors
    }
}

public bool:IsValidClient(client) 
{
    if(client <= 0)
        return false;
    if(client > MaxClients)
        return false;

    return IsClientInGame(client);
} 

public bool:TraceEntityFilterPlayer(entity, contentsMask, any:data) 
{
	return entity > MaxClients;
}