• Jump Range: Because Rats are assigned based on how quickly they can reach a client, maximizing jump range is a good idea.  We highly recommend a minimum 20Ly jump range before going on rescues or requesting a drill. A more reasonable range for 3-5 jumps to a typical case in the bubble is 40ly.
• Fuel Scoop: Our clients often end up in uninhabited space, and every limpet you give to the client takes 1 ton of fuel out of your tank.  Without a fuel scoop … you will soon find yourself in serious trouble.
• Fuel Transfer Limpet Controller:  This is what programs, launches and guides the limpets on their way to the client.  Class ‘A’ controllers are preferred for their range, which can make a difference if the client is moving for some reason or if you get dropped further from the client.
• Limpets: All is nice and well, yet without limpets, your shiny ship would be very, very useless. Don’t forget to resupply your stock through [ADVANCED MAINTENANCE → RESTOCK] at a station’s menu. You should carry at least 8 limpets, although consider that a reasonable minimum.  Ships with a class 7 FSD, for example, can be very fuel hungry – twelve limpets might only just be enough to get such a client fuel for one jump. In a pinch limpets can be synthesized: 10 Iron + 10 Nickel for 4 limpets.
• Cargo Hold: Limpets need space to be stored in, so you need a cargo hold with enough storage space (1t per limpet).  It's recommended that a minimum of 8 limpets are carried.  Most Rats carry 12-16 limpets.  Remember that too many limpets will lower your jump range.

• Supercruise Overcharge FSD This is only available on live game modes. But since it is a straight upgrade over the regular FSD, there is no downside to installing it. This module will allow you to reach clients that are 100 kls away in seconds which would require multiple minutes before. Beware the increased fuel drain rate. Some ships are more optimized for SCO than others with respect to fuel usage and cockpit shake.
• Extra Fuel tanks are optional and depend mainly on the class of your Ratship. Note that increased fuel capacity reduces plottable jump range.  This is most useful on an Anaconda or Mandalay built for Long Range Rescues, when using the spansh neutron plotter.
• Weapons are not required. You are free to take them with you, of course, and in some cases they can save the client from hostile NPCs.  However, they reduce your jump range, so consider how many you fit, and look into lightweight engineering.  Consider investing in stronger defensive mechanisms  such as shield boosters, chaff and/or heat sinks.  We usually do not run into trouble from other CMDRs through rescues, yet it happens (very, very seldom).  It's more likely that you'll run into an NPC attempting to take cargo or claim a bounty.  In such situations, if an NPC becomes hostile towards the client, using your weapons to draw the NPC away to attack you instead can buy the client the time for their shields to recharge or escape.
• Repair/Decontamination Limpet Controllers Occasionally you will encounter clients with low hull integrity, or they might request a repair right away. Restoring at least a bit of their hull could help them reach a station safely. Decontamination Limpets can also repair a ship, in addition they can clear the caustic status, which can be helpful when saving clients in active Thargoid areas. There is also the rescue limpet controller, it essentially trades weight and limpet range for slot efficiency.
• AFMU if you build your ratship with long range rescues in mind and you intend to use supercharging from neutrons your FSD will degrade each jump. Below 80% integrity you will experience random FSD malfunctions. Use the AFMU to repair the FSD if that happens. The AFMU uses a lot of power, but can be disabled while you are not using it.

 Example Builds

Below are some examples of builds across the whole budget range. There are 2 builds per example: one Unengineered and one engineered. The engineering for these examples only need access to Felicity Farseer and include the Guardian Frameshift Drive Booster.
These examples are not fully optimized and are intended to give a nice starting point to build your own ratship.

Builds for Legacy Elite 

The following builds are good options for Legacy PC as well as XBox and Playstation. They of course work just as well in Horizons and Odyssey.

Builds for Live Elite 

The recommended ships for live elite come with better SCO performance and overall buffed stats in pretty much every category.