How do I make it cost gas instead of minerals hehe..

Repair price and repair speed is based off of build time and build price, so change the cost to only gas, and it costs only gas to repair.

Ok so if it's a siege tank, make the cost of the siege tank x gas with x build time?

Yes.

But keep in mind repair cost is only a percentage of the build cost.
I don't know how much actually, but something around 25-50%.

So like if it cost 5 gas to build, it would repair for 1 gas?

something like that - duh

I tried testing once, I forgot what the amount was, but how fast you repair is based on the time to build, and the amount is based on the base cost.

That's why heroes have gas/mineral/time costs.

According to the test I just did, it requires 1/3 as many minerals/gas to repair as it does to build. Example: Something costs 1000 minerals, it will cost 333 minerals to repair from 1 hp to full.