I've been playing with floorplans for a few years... started on camper designs, then decided to look into motor coach designs. I started doing skoolie plans about a year ago. This one is based on an actual AmTran RE 12 windows bus I shopped for a while (I've been measuring by #windows rather than #rows or #passengers).
Here are my assumptions:
Windows are 30" wide on center.
Windows are all same width (I know that's not true for all builds).
1 seating row = 1 window... would need to stretch that for comfort.
Link to image on Google Drive
Here is my layout, by cabin section:
1. COCKPIT. Not shown... this is everything "behind the white line".
2. SEATING/DINING. I'll use bus seats for this area. 2 dinettes side by side allows the whole family to eat together at once... novel concept! I've assumed that when I flip the rear facing seats around that I'll need to add some leg room to the dinette area. I don't know how much to add, though, so this is a guess. I will install some seatbelts and LATCH anchors on the forward facing seats (including the dinettes).
3. GALLEY KITCHEN. We don't cook in the camper, and we won't in the skoolie. I will not install a range/oven (no need for propane)... I can use a Coleman portable outside for that purpose. We eat cold cereal or bagels for breakfast, sandwiches for lunch, and dinner out a local place (or leftovers). In lieu of the standard RV fridge I'll use 2x 12V coolers... 80 Qt for a fridge, and a 40 Qt for a freezer. The sink cabinet will house the water heater (Webasco?) and water pump.
4. KIDS'QUARTERS. Still working on designs here. This plan uses 4x Army stretchers for top/middle bunks, with an IKEA small bed mattress on the floor for the bottom bunk (some of the best sleep I've ever gotten was on those stretchers!). The stretchers might be able to be folded up against the wall to create a play area on rainy days. I will block out the windows in this area to keep the kids from being up against a drafty wall. The bottom bunk won't be as long as the tops due to the rear wheel well.
5. LATRINE. Planning to do a wet bath, since only the toddlers and infants will use it for showering... all others can use campground shower facilities. If we're boon docking I'll carry a pop up shower stall and use a spigot on the outside of the bus (will have to tap into the hot water line with this!). Counter top (with small sink) will sit over wheel well. I'll do a combined black/grey tank below the rear wheels... I think I can get the kitchen sink to drain that far successfully, and I want the grey in there to dissolve all the toilet paper my 5 year old uses!
6. MASTER BEDROOM. Full size bed (camping should bring us closer, whether we like it or not!). We use laundry baskets (18x24") as luggage in the camper, and we'll continue that in the skoolie. Baskets will slide under our bed, and the cabinet will be built to shelve several baskets stacked.
7. HVAC. I'll install 2x roof mounted AC's (13.5 or 15 kBTU?), preferably in the emergency hatch holes already in the roof (I'm allergic to holes in the roof). I'd like to run the front one on the alternator while cruising (to avoid the necessity for a jenny), and the rear one on less than 20A (so I can plug in anywhere and still sleep comfortably without blowing breakers). Heating is my last concern. I'd like to avoid propane altogether... heat would be no problem while cruising, but how to heat while docked is still a mystery to me.
8. ELECTRIC. I'm trying to keep everything 12V DC as much as possible. The only exceptions will be the rear AC, the microwave, and 1x outlet for hairdryer and other limited use appliances (toaster?). I might run the microwave and outlet on an inverter. I want a huge battery bank for up to 3 days of dry camping. Will use LED lighting.
9. PLUMBING. Balancing weights concerns me, but I don't know that it should. I'd like a 100 gallon capacity... that's over 800# of weight! How important is it to balance that load left/right and fore/aft? The only hole I'll put in the roof is for the plumbing vent... will use a marine grade vent cap for that application (I've seen someone do that... Von Slatt, maybe?).