It is difficult to figure out how to write Ogham in a modern context, without understanding at least something of the history of Ogham.

Ogham script is an ancient form of writing that originated in Ireland around the 300 - 400s CE. It was used for centuries to record on stone the names of people, tribes, and ancestry, before moving to the manuscript tradition from about the 700s CE.

So, Ogham was both carved and written. Within these two different periods of Ogham, Ogham was written differently.

How To Write Ogham Vertically

In the earliest phase of stone inscription, which is referred to variously as Classical, Orthodox, or Monumental Ogham, the letters, words and phrases were carved into stone pillars vertically, from bottom to top. The edge of a stone was most often used as a central 'stem line', and the Ogham Alphabet was marked in strokes or notches around it.

Auraicept na N-Éces, the Scholars Primer, describes the groups this way, when written vertically:

These are their signs: right of stem, left of stem, athwart of stem, through stem, about stem. Thus is a tree climbed, to wit, treading on the root of the tree first with thy right hand first and thy left hand after. Then with the stem, and against it, and through it, and about it.

From earliest times, then, the Ogham was written from bottom to top, as a tree is climbed.

How to Write Ogham Horizontally

Manuscripts were being produced from Early Christian monasteries which included the monks reworking of the Ogham. Their native script was preserved and used, sometimes at the top of manuscript pages to annotate and display scholars' names. Perhaps they wanted to place their own traditions and scholarship right alongside the classical Greek and Roman alphabets they were expected to work with?

Within the Manuscript tradition, sometimes referred to as the Scholastic Ogham, the writing shifted from vertical to horizontal. Some written inscriptions contain an arrow at the beginning, to denote the orientation or direction in which the inscription should read, but the majority would have followed from left to right. Ogham was studied and used in this way from about the 800s CE right through to the 1500 and even 1600s CE. 

During this period, the alphabet was expanded to include five/six additional characters, known as the Forfeda or Extra Letters.

Can You Write English Words or Names in Ogham?

Using the Ogham alphabet to write English words doesn't really work out, for a number of reasons.

For a start, Ogham was developed for the Irish language, and each Ogham Fid (letter) represents one syllable or sound. In its earliest form, the alphabet was designed to represent what is known as 'Primitive Irish', which didn't have the letter P.

In later stages, manuscript scholars developed a letter for the P sound, or rather, two of them. First there was the Pín or Iphín letter of the Forfeda, and afterwards an extra extra letter in the form of Peith, which is a modified form of the initial letter Beith.

Modern Irish never developed a direct equivalent for the letters J, K, V, W, X, and Y, which are all still absent from Ogham.

There are also some letters and sounds which are different from the typical Latin alphabet which English uses, for example F and V being similar (Fern), nG (nGétal) as a single letter, and Z represented as St (Straif). 

All in all, it is best to translate an English word or name into Irish - Modern Irish will do fine for this purpose - or as close as possible. Once you have the Irish to hand, you will be able to write the Ogham. 

Helpful Resources

• To help with translation as you figure out how to write Ogham, here is a good online dictionary.
• To do the transliteration of an Irish word to Ogham, here is an Ogham Letters Cheat Sheet.