The shed is 20 feet long and contains six "tracks" made of 2x6 grooved boards to save on track expense. Additionally another 2x6 track is located in the attic area for more storage. This gives 120' of storage on the main level with 20' more on the attic shelf. A maximum of 2 shelves can be placed in the attic area and still have reasonable access via the roof hatches to the tracks below. Probably as many as four shelves could be placed there if additional access was provided through the side walls for the lower level. I chose to minimize the number of doors to better weatherise the structure. As configured it should hold around 100 cars of "normal" size, a bit less if full size 1:20.3. The shed has given excellent protection to the rolling stock through 3 years now and cars are kept in it all year long.
The 2x6 tracks use 3/16" grooves to accomodate the wheel flanges. A 3/16" router bit or the 1/8" blade and a 1/16" chipper from a dado set on a table saw does a good job cutting the grooves. Be sure the grooves are in gauge and make the grooves deep enough to allow for at least some debris to collect in them and still clear the bottoms of the wheel flanges. If you are using close to scale tread width on your wheels then you might have to cut the grooves narrower than 3/16" to prevent the wheels from falling into the grooves or lay rail. Remember that the wood will swell and move some so the wider you can make the grooves without the wheels falling in the better. Be sure and run several small samples first and test them until you get what works for you. The successful sample can be used as a gauge to set up for making the rest.
My shed is located above ground level for good drainage and ventilation. I recommend this to you if possible. If the shed must be placed at ground level then dig out beneath where the shed will be and install drain rock and trench to give the water some place to go. You don't want dampness and mildew to damage the structure. For good safe storage it needs both drainage and ventilation to protect both the contents and the structure itself. In this case you might want to include additional vents on either end of the structure for better airflow. I haven't needed them up here even in the damp northwest with my raised structure as there is plenty of airflow through the landscape fabric floor alone.
The roof is fiberglass and can be any color you choose. If you live in a hot area you may want to make your roof more opaque than I did as heat can build up fast inside. A regular plywood roof with roofing felt or asphalt shingles would work just as well but you might need to provide for an interior light. Also ventilation openings on the eave ends would help cool things down a bit. The fiberglass allows a lot of light through and illuminates the interior quite well. I have several resident lizards in the shed for much of the year. Even when it is cool outside they'll be sitting atop my rolling stock with legs outstretched enjoying the country club atmosphere. Aside from a little lizard poop on the car roofs they don't hurt anything and keep the insect population down.
Most of the structure is put together using p.t. lumber and 2-1/2" or 3" galvanised deck screws. I only used p.t. lumber for the floor and track sections. The rest of the structure used regular 2x4 stud material. The outside is sheathed with 1/2" (not 3/8" as stated elsewhere) T-111 siding. This is actually made for interior use but, painted, has held up quite well. I used it because I already had it on hand from a previous job. Use 5/8" T-111 if you have to buy it for the project. Costs a little more but is specifically made to be used as exterior siding. Of course you may use your own favorite siding if you wish. Other materials are listed in the article.
Caveat: I've found that about the maximum distance I can push cars inside the shed through the wooden grooves without risk of derailment is about 12' to 14'. Friction and rolling resistance is more than twice what it would be on rails. Still the 20' length works well if the cars are pushed in in two strings and given a helping hand through one of the roof hatches. The additional capacity outweighs the minor inconvenience. Of course you may opt for a shorter version anyway depending on need ans space available.
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