You can't just put gerbils together immediately but need to use a split cage over several weeks to introduce them. Only links I know of are on breeders sites but with a split cage you take an aquarium or plastic storage container and slide a mesh divider through the middle. Put 1 gerbil on each side. If using a storage container cut out the middle of the lid and cover it in mesh and if using an aquarium buy a mesh top to provide ventilation. Plastic containers are also useful because you can staple the mesh down the inside of the container with a good quality stapler, cut the mesh off when putting the gerbils together, and then throw the container out or put it to another use and get a new one since they are so cheap. The gerbils will chew out the staple holes if you try to use the container longterm after removing the mesh. Switch which side the gerbils are on every day or 2 for several weeks. The next step is debated. Some say strip the cage down and wipe with vinegar to remove all scents before attempting to put the gerbils together without the divider. Others say to switch them a couple times in the same day so they can't lay claim to either side and their scent is equally on both sides before removing the divider and letting them find each other. Personally I tend to use the 2nd way more frequently than stripping the cage. Mesh is often called hardware cloth if you go to a hardware store to get it.
I know it's highly debated but I like to use aquariums or storage containers for permanent cages because I have found nothing else of appropriate size that doesn't cost a fortune. Although aquariums aren't extremely cheap but if you keep an eye out you can get used ones for pretty cheap and just disinfect with vinegar before use. Most plastic cages with tubes are either too small or easily chewed out of. Most wire cages are too small, cost a fortune, and allow the bedding to fly out. Being diggers gerbils love deep bedding and that can't be accomplished in wire or open sided cages. I have never had ventilation issues so long as the cage is appropriately sized and the top is mesh. Currently my 2 females are in a 40gallon aquarium I got for $40 from a reptile store that was going out of business. The most successful gerbil keepers I know use either custom built glass cages or modified storage containers where the plastic lid has been replaced with mesh. I suggest around 30gallons for 2 gerbils and if using an aquarium a 20gallon long(not standard or tall) minimum might work. Convert storage containers from litres by just typing in " x litres to gallons" in google.com where x is the amount your converting in order to get an idea how that compares to aquarium sizes.
