I'm going to agree with the "Same rate as engineers" comments before me. I think anything else is open to exploitation, and this is why engineers gain at the rate they do.
Has everyone forgotten the squad points? Scout + Engie in your squad = lots and lots of points... Sure, maybe it would be nice to get points for building stuff if you're not an engie, but that's not your main cause for being that task. Not only do engies get the highest point count, but you also see them with the highest death count too (if you're a ninja engie that is, by yourself building refs on the other side of the map =P). Tbh, it's not too bad. And if the comm is finding it hard to build stuff, then maybes you should start shouting at your team to go engie rather than all grenadiers and riflemen eh?
my team hardly die now adays, and when they do we have an apc or alike at the front lines in the middle of enermy fire... and if the half assed newbies knew what enginers actually do, it would help